Types of sticks microbiology. Modern classification of bacteria
What are bacteria: types of bacteria, their classification
Bacteria are tiny microorganisms that have been around for thousands of years. It is impossible to see microbes with the naked eye, but we should not forget about their existence. There are a huge number of bacilli. The science of microbiology is engaged in their classification, study, varieties, features of structure and physiology.
Microorganisms are called differently, depending on their kind of actions and functions. Under a microscope, you can observe how these little creatures interact with each other. The first microorganisms were rather primitive in form, but their importance should by no means be underestimated. From the very beginning, bacilli evolved, created colonies, tried to survive in changing climatic conditions. Different vibrios are able to exchange amino acids in order to grow and develop normally as a result.
Today it is difficult to say how many species of these microorganisms are on earth (this number exceeds a million), but the most famous and their names are familiar to almost every person. It doesn’t matter what microbes are and what they are called, they all have one advantage - they live in colonies, so it is much easier for them to adapt and survive.
First, let's figure out what microorganisms exist. The simplest classification is good and bad. In other words, those that are harmful to the human body, cause many diseases and those that are beneficial. Next, we will talk in detail about what are the main beneficial bacteria and give a description of them.
You can also classify microorganisms according to their shape, characteristics. Probably, many people remember that in school textbooks there was a special table with the image of various microorganisms, and next to it was the meaning and their role in nature. There are several types of bacteria:
- cocci - small balls that resemble a chain, as they are located one behind the other;
- rod-shaped;
- spirilla, spirochetes (have a convoluted shape);
- vibrios.
Bacteria of different shapes
We have already mentioned that one of the classifications divides microbes into species depending on their shape.
Bacteria coli also have some features. For example, there are types of rod-shaped with pointed poles, with thickened, with rounded or with straight ends. As a rule, rod-shaped microbes are very different and are always in chaos, they do not line up in a chain (with the exception of streptobacilli), they do not attach to each other (except for diplobacilli).
To microorganisms of spherical forms, microbiologists include streptococci, staphylococci, diplococci, gonococci. It can be pairs or long chains of balls.
Curved bacilli are spirilla, spirochetes. They are always active but do not produce spores. Spirilla is safe for people and animals. You can distinguish spirilla from spirochetes if you pay attention to the number of curls, they are less convoluted, have special flagella on the limbs.
Types of pathogenic bacteria
For example, a group of microorganisms called cocci, and in more detail streptococci and staphylococci cause real purulent diseases (furunculosis, streptococcal tonsillitis).
Anaerobes live and develop perfectly without oxygen; for some types of these microorganisms, oxygen generally becomes deadly. Aerobic microbes need oxygen to survive.
Archaea are almost colorless unicellular organisms.
Pathogenic bacteria should be avoided because they cause infections, gram-negative microorganisms are considered resistant to antibodies. There is a lot of information about soil, putrefactive microorganisms, which are harmful, useful.
In general, spirilla are not dangerous, but some species can cause sodoku.
Varieties of beneficial bacteria
Even schoolchildren know that bacilli are useful and harmful. People know some names by ear (staphylococcus, streptococcus, plague bacillus). These are harmful creatures that interfere not only with the external environment, but also with humans. There are microscopic bacilli that cause food poisoning.
Must know useful information about lactic acid, food, probiotic microorganisms. For example, probiotics, in other words good organisms, are often used for medical purposes. You ask: for what? They don't allow harmful bacteria multiply inside a person, strengthen the protective functions of the intestine, have a good effect on the human immune system.
Bifidobacteria are also very beneficial for the intestines. Lactic acid vibrios include about 25 species. In the human body, they are present in large quantities, but are not dangerous. On the contrary, they protect gastrointestinal tract from putrefactive and other microbes.
Speaking of good ones, one cannot fail to mention the huge species of streptomycetes. They are known to those who took chloramphenicol, erythromycin and similar drugs.
There are microorganisms such as Azotobacter. They live in the soil for many years, have a beneficial effect on the soil, stimulate the growth of plants, cleanse the earth of heavy metals. They are irreplaceable in medicine, agriculture, medicine, food industry.
Types of bacterial variability
By their nature, microbes are very fickle, they die quickly, they can be spontaneous, induced. We will not go into details about the variability of bacteria, since this information is of more interest to those who are interested in microbiology and all its branches.
Types of bacteria for septic tanks
Residents of private homes understand the urgent need to treat wastewater, as well as cesspools. Today, drains can be quickly and efficiently cleaned with the help of special bacteria for septic tanks. For a person, this is a huge relief, since cleaning the sewer is not a pleasant thing.
We have already clarified where the biological type of wastewater treatment is used, and now let's talk about the system itself. Bacteria for septic tanks are grown in laboratories, they kill the unpleasant smell of drains, disinfect drainage wells, cesspools, reduce the volume Wastewater. There are three types of bacteria that are used for septic tanks:
- aerobic;
- anaerobic;
- live (bioactivators).
Very often people use combined cleaning methods. Strictly follow the instructions on the preparation, make sure that the water level contributes to the normal survival of bacteria. Also, remember to use the drain at least once every two weeks so that the bacteria have something to eat, otherwise they will die. Don't forget that chlorine from cleaning powders and liquids kills bacteria.
The most popular bacteria are Dr. Robik, Septifos, Waste Treat.
Types of bacteria in urine
In theory, there should be no bacteria in the urine, but after various actions and situations, tiny microorganisms settle where they please: in the vagina, in the nose, in water, and so on. If the bacteria were found during the tests, this means that the person is suffering from diseases of the kidneys, bladder or ureters. There are several ways in which microorganisms enter the urine. Before treatment, it is very important to investigate and accurately determine the type of bacteria and the route of entry. This can be determined by biological urine culture, when the bacteria are placed in a favorable habitat. Next, the reaction of bacteria to various antibiotics is checked.
We wish you to always stay healthy. Take care of yourself, wash your hands regularly, protect your body from harmful bacteria!
The modern classification (grouping) of microorganisms was proposed in 1980 by an American microbiologist bergy. According to this classification, the whole world of microbes is divided into three kingdoms: bacteria, fungi, viruses.
Who are they? To find out, I went to the school library, where our librarian helped me to work through the literature in search of an answer.
Name microorganisms comes from the Latin word micros - small. Therefore, microorganisms (microbes) are unicellular organisms less than 0.1 mm in size, which cannot be seen with the naked eye.
Appeared on Earth many billions of years before the appearance of man! They have a variety of shapes. Some are immobile, while others have cilia or flagella with which they move.
Most microbes breathe air aerobes.
For others, the air is harmful - it is anaerobes.
In the world classification, microbes are divided into pathogenic(pathogenic) and non-pathogenic microbes. These include bacteria, viruses, lower microscopic fungi (mucor, yeast) and algae, protozoa (
).
Attachment 1
Classification of microorganisms
From the lessons of the world around me, I learned that bacteria, previously considered microscopic plants, are now separated into an independent kingdom of Bacteria - one of four in the current classification system, along with plants, animals, fungi.
(other Greek - stick) - these are unicellular microorganisms, characterized by cellular similarities, having a variety of shapes: spherical - cocci, rod-shaped - bacilli, curved - vibrios, spiral - spirilla, in the form of a chain - streptococci, in the form of clusters - staphylococci (
).
Appendix 2
Classification of bacteria by shape
| bacterium name | Bacteria shape | Bacteria image |
| cocci | spherical | |
| Bacillus | rod-shaped | |
| Vibrio | curved, comma |  |
| Spirillum | Spiral |  |
| streptococci | Chain |  |
| Staphylococci | bunches |  |
| diplococci | Two round bacteria in one capsule |
About ten thousand species of bacteria have been described so far. The branch of microbiology deals with the study of bacteria bacteriology.
(lat. virus poison) - the most primitive organisms on earth with a size of 20-300 nm. They reproduce only inside the living cells of the body. They do not have a cellular structure. In the free state, no metabolic processes occur in them.
(lower) are unicellular fungi. These mushrooms include the well-known white mold ( mukor mushroom). Such a fungus often develops on bread or vegetables and looks at first like cotton wool - a white fluffy substance that gradually turns black. Despite the fact that in everyday life mucor causes damage, in nature it plays a useful function, decomposing dead organisms.
A special niche in microbiological research is occupied by a group of unicellular fungi that live in a liquid medium, rich in organic matter used in fermentation processes.
(cyanobacteria) is a type of the oldest large bacteria capable of photosynthesis, accompanied by the release of oxygen.
- many different organisms, the body of which consists of a single cell ( infusoria, amoeba, green euglena...).
Thus, according to the classification I have considered, there is a huge number of microorganisms that exist and multiply in conditions that are comfortable for each species. Each type of microorganisms will depend on the habitat and perform certain functions.
The concept of microorganisms
Microorganisms are organisms invisible to the naked eye due to their small size.
The size criterion is the only one that unites them.
Otherwise, the world of microorganisms is even more diverse than the world of macroorganisms.
According to modern taxonomy, microorganisms to 3 kingdoms:
- Vira - viruses;
- Eucariotae - protozoa and fungi;
- Procariotae - true bacteria, rickettsia, chlamydia, mycoplasmas, spirochetes, actinomycetes.
Just as for plants and animals, the name of microorganisms is used binary Nomenclature, i.e. generic and specific name.
If the researchers cannot determine the species affiliation and only the belonging to the genus is determined, then the term species is used. Most often, this occurs when identifying microorganisms that have non-traditional nutritional needs or living conditions. Genus name usually either based on the morphological trait of the corresponding microorganism (Staphylococcus, Vibrio, Mycobacterium), or is derived from the name of the author who discovered or studied this pathogen (Neisseria, Shig-ella, Escherichia, Rickettsia, Gardnerella).
specific name often associated with the name of the main disease caused by this microorganism (Vibrio cholerae - cholera, Shigella dysenteriae - dysentery, Mycobacterium tuberculosis - tuberculosis) or with the main habitat (Escherihia coli - Escherichia coli).
In addition, in Russian medical literature it is possible to use the corresponding Russified name of bacteria (instead of Staphylococcus epidermidis - epidermal staphylococcus; Staphylococcus aureus - Staphylococcus aureus, etc.).
Kingdom of prokaryotes
includes the department of cyanobacteria and the department of eubacteria, which, in turn, subdivided intoorders:
- actually bacteria (departments Gracilicutes, Firmicutes, Tenericutes, Mendosicutes);
- actinomycetes;
- spirochetes;
- rickettsia;
- chlamydia.
Orders are divided into groups.
prokaryotes differ from eukaryote because Dont Have:
- morphologically formed nucleus (there is no nuclear membrane and there is no nucleolus), its equivalent is the nucleoid, or genophore, which is a closed circular double-stranded DNA molecule attached at one point to the cytoplasmic membrane; by analogy with eukaryotes, this molecule is called a chromosomal bacterium;
- mesh apparatus of Golgi;
- endoplasmic reticulum;
- mitochondria.
There is also a number of signs or organelle, characteristic of many, but not all prokaryotes, which allow distinguish them from eukaryotes:
- numerous invaginations of the cytoplasmic membrane, which are called mesosomes, they are associated with the nucleoid and are involved in cell division, sporulation and respiration of the bacterial cell;
- a specific component of the cell wall is murein, according to the chemical structure it is peptidoglycan (diaminopiemic acid);
- Plasmids are autonomously replicating ring-shaped molecules of double-stranded DNA with a molecular weight smaller than the bacterial chromosome. They are located along with the nucleoid in the cytoplasm, although they can be integrated into it, and carry hereditary information that is not vital for the microbial cell, but provides it with certain selective advantages in environment.
Most famous:
F-plasmids providing conjugation transfer
between bacteria;
R-plasmids are drug resistance plasmids that circulate among bacteria genes that determine resistance to chemotherapeutic agents used to treat various diseases.
bacteria
Prokaryotic, predominantly unicellular microorganisms that can also form associations (groups) of similar cells, characterized by cellular but not organismal similarities.
Basic taxonomic criteria,allowing to assign bacterial strains to one or another group:
- morphology of microbial cells (cocci, rods, convoluted);
- relation to Gram stain - tinctorial properties (gram-positive and gram-negative);
- type of biological oxidation - aerobes, facultative anaerobes, obligate anaerobes;
- ability to spore.
Further differentiation of groups into families, genera and species, which are the main taxonomic category, is carried out on the basis of the study of biochemical properties. This principle is the basis for the classification of bacteria given in special guidelines - determinants of bacteria.
View is an evolutionarily established set of individuals with a single genotype, which under standard conditions is manifested by similar morphological, physiological, biochemical characteristics.
For pathogenic bacteria, the definition of "species" is supplemented by the ability to cause certain nosological forms of diseases.
Exists intraspecific differentiation of bacteriaon theoptions:
- according to biological properties - biovars or biotypes;
- biochemical activity - fermenters;
- antigenic structure - serovars or serotzhy;
- sensitivity to bacteriophages - fagovars or phage types;
- resistance to antibiotics - resistant products.
Widely used in microbiology special terms- culture, strain, clone.
culture is a collection of bacteria visible to the eye on nutrient media.
Cultures can be pure (a set of bacteria of one species) and mixed (a set of bacteria of 2 or more species).
Strain is a collection of bacteria of the same species isolated from different sources or from the same source at different times.
Strains may differ in some characteristics that do not go beyond the characteristics of the species. Clone- a collection of bacteria that are the offspring of a single cell.
Bacteria are prokaryotic microorganisms of the cellular structure. Their sizes are from 0.1 to 30 microns. Microbes are extremely common. They live in soil, air, water, snow and even hot springs, on the body of animals, as well as inside living organisms, including the human body.
The distribution of bacteria into species is based on several criteria, among which the shape of microorganisms and their spatial distribution are most often taken into account. So, according to the shape of the cells, bacteria are divided into:
Coci - micro-, diplo-, strepto-, staphylococci, as well as sarcins;
Rod-shaped - monobacteria, diplobacteria and streptobacteria;
Convoluted species - vibrios and spirochetes.
Burgey's determinant systematizes all known bacteria according to the principles of bacterial identification that have found the widest distribution in practical bacteriology, based on differences in the structure of the cell wall and in relation to Gram stain. The description of bacteria is given by groups (sections), which include families, genera and species; in some cases, groups include classes and orders. Bacteria pathogenic to humans are included in a small number of groups.
The key distinguishes four main categories of bacteria -
Gracillicutes [from lat. gracilis, graceful, thin, + cutis, skin] - species with a thin cell wall, stained gram negative;
firmicutes [from lat. flrmus, strong, + cutis, skin] - bacteria with a thick cell wall, staining gram positive;
Tenericutes [from lat. tener, gentle, + cutis, skin] - bacteria lacking a cell wall(mycoplasmas and other members of the class Mollicutes)
Mendosicutes [from lat. mendosus, irregular, + cutis, skin] - archaebacteria (methane- and sulfate-reducing, halophilic, thermophilic and archaebacteria, devoid of a cell wall).
Group 2 Burgey's determinant. Aerobic and microaerophilic motile convoluted and curved Gram-negative bacteria. Species pathogenic for humans are included in the genera Campylobacter, Helicobacters Spirillum.
Group 3 of Bergey's determinant. Non-motile (rarely motile) Gram-negative bacteria. Does not contain pathogenic species.
Group 4 of Burgey's determinant. Gram-negative aerobic and microaerophilic rods and cocci. Species pathogenic for humans are included in the Legionellaceae, Neisseriaceae and Pseudomonada-ceae families, the group also includes pathogenic and opportunistic bacteria of the genera Acinetobacter, Afipia, Alcaligenes, Bordetella, Brucella, Flavobacterium, Francisella, Kingella and Moraxella.
Group 5 of Bergey's determinant. Facultative anaerobic Gram-negative rods. The group is formed by three families - Enterobacteriaceae, Vibrionaceae and Pasteurellaceae, each of which includes pathogenic species, as well as pathogenic and opportunistic bacteria of the genera Calymmobaterium, Cardiobacterium, Eikenetta, Gardnerella and Streptobacillus.
Group 6 of Bergey's determinant. Gram-negative anaerobic straight, curved and spiral bacteria. Pathogenic and opportunistic species are included in the genera Bacteroides, Fusobacterium, Porphoromonas and Prevotelta.
Group 7 of Bergey's determinant. Bacteria that perform dissimilation reduction of sulfate or sulfur Does not include pathogenic species.
Group 8 of Bergey's determinant. Anaerobic Gram-negative cocci. Includes opportunistic bacteria of the genus Veillonella.
Group 9 of Bergey's determinant. Rickettsia and chlamydia. Three families - Rickettsiaceae, Bartonellaceae and Chlamydiaceae, each of which contains species pathogenic to humans.
Groups 10 and 11 of the Burgey's guide include anoxy- and oxygenic phototrophic bacteria that are not pathogenic to humans.
Group 12 of Burgey's determinant. Aerobic chemolithotrophic bacteria and related organisms. It combines sulfur-iron- and manganese-oxidizing and nitrifying bacteria that do not cause damage to humans.
Groups 13 and 14 of Burgey's guide include budding and/or outgrowth bacteria and sheath-forming bacteria. Represented by free-living species, not pathogenic for humans;
Groups 15 and 16 of the Burgey's guide unite gliding bacteria that do not form fruiting bodies and form them. The groups do not include species pathogenic to humans.
Group 17 of Burgey's determinant. Gram-positive cocci. Includes opportunistic species of the genera Enterococcus Leuconostoc, Peptococcus, Peptostreptococcus, Sarcina, Staphylococcus, Stomatococcus, Streptococcus.
Group 18 of Burgey's determinant. Spore-forming Gram-positive rods and cocci. Includes pathogenic, conditionally pathogenic rods of the genera Clostridium and Bacillus.
Group 19 of Burgey's determinant. Spore-forming Gram-positive rods of regular shape. Including opportunistic species of the genera Erysipelothrix and Listeria.
Group 20 of Burgey's determinant. Irregularly shaped spore-forming Gram-positive rods. The group includes pathogenic and opportunistic species of the genera Actinomyces, Corynebacterium Gardnerella, Mobiluncus, etc.
Group 21 of Burgey's determinant. Mycobacteria. Includes the only genus Mycobacterium, which combines pathogenic and opportunistic species.
Groups 22-29. Actinomycetes. Among numerous species, only nocardioform actinomycetes (Group 22) of the genera Gordona, Nocardia, Rhodococcus, Tsukamurella, Jonesia, Oerskovi, and Terrabacter are capable of causing lesions in humans.
Group 30 of Burgey's determinant. Mycoplasmas. Species included in the genus Acholeplasma, Mycoplasma and Ureaplasma are pathogenic for humans.
The remaining groups of Bergey's determinant - methanogenic bacteria (31), sulfate-reducing bacteria (32 extremely halophilic aerobic archaebacteria (33), archaebacteria devoid of a cell wall (34), extreme thermophiles and hyperthermophiles, metabolizing sulfur (35) - do not contain species pathogenic to humans.
2.1. Systematics and nomenclature of microbes
The world of microbes can be divided into cellular and non-cellular forms. Cellular forms of microbes are represented by bacteria, fungi and protozoa. They can be called microorganisms. Non-cellular forms are represented by viruses, viroids and prions.
The new classification of cellular microbes includes the following taxonomic units: domains, kingdoms, types, classes, orders, families, genera, species. The classification of microorganisms is based on their genetic relationship, as well as morphological, physiological, antigenic and molecular biological properties.
Viruses are often considered not as organisms, but as autonomous genetic structures, so they will be considered separately.
The cellular forms of microbes are divided into three domains. Domains bacteria and Archaebacteria include microbes with a prokaryotic type of cell structure. Domain Representatives Eukarya are eukaryotes. It consists of 4 kingdoms:
Mushroom kingdoms (Fungi, Eumycota);
protozoan kingdoms (Protozoa);
kingdoms Chromista(chrome);
Microbes with unspecified taxonomic position (Microspora, microsporidia).
Differences in the organization of prokaryotic and eukaryotic cells are presented in table. 2.1.
Table 2.1. Signs of a prokaryotic and eukaryotic cell
2.2. Classification and morphology of bacteria
The term "bacteria" comes from the word bacteria, what does wand mean. Bacteria are prokaryotes. They are divided into two domains: bacteria and Archaebacteria. Bacteria in the domain archaebacteria, represent one of the oldest forms of life. They have structural features of the cell wall (they lack peptidoglycan) and ribosomal RNA. Among them, there are no pathogens of infectious diseases.
Within the domain, bacteria are subdivided into the following taxonomic categories: class, phylum, order, family, genus, species. One of the main taxonomic categories is species. A species is a collection of individuals that have a common origin and genotype, united by similar properties that distinguish them from other members of the genus. The species name corresponds to the binary nomenclature, i.e. consists of two words. For example, the causative agent of diphtheria is written as Corynebacterium diphtheriae. The first word is the name of the genus and is written with capital letter, the second word denotes the species and is written with a lowercase letter.
When a species is mentioned again, the generic name is abbreviated to the initial letter, for example C. diphtheriae.
A set of homogeneous microorganisms isolated on a nutrient medium, characterized by similar morphological, tinctorial (relation to dyes), cultural, biochemical and antigenic properties, is called pure culture. A pure culture of microorganisms isolated from a specific source and different from other members of the species is called strain. Close to the concept of "strain" is the concept of "clone". A clone is a collection of offspring grown from a single microbial cell.
To designate some sets of microorganisms that differ in certain properties, the suffix “var” (variety) is used, therefore, microorganisms, depending on the nature of the differences, are designated as morphovars (difference in morphology), resistant products (difference in resistance, for example, to antibiotics), serovars (difference in antigens), fagovars (difference in sensitivity to bacteriophages), biovars (difference in biological properties), chemovars (difference in biochemical properties), etc.
Previously, the basis of the classification of bacteria was the structural feature of the cell wall. The subdivision of bacteria according to the structural features of the cell wall is associated with the possible variability of their coloration in one color or another according to the Gram method. According to this method, proposed in 1884 by the Danish scientist H. Gram, depending on the staining results, bacteria are divided into gram-positive, stained blue-violet, and gram-negative, stained red.
Currently, the classification is based on the degree of genetic relationship, based on the study of the structure of the ribosomal RNA (rRNA) genome (see Chapter 5), determining the percentage of guanine-cytosine pairs (GC-pairs) in the genome, constructing a genome restriction map, and studying the degree of hybridization. Phenotypic indicators are also taken into account: attitude to Gram stain, morphological, cultural and biochemical properties, antigenic structure.
Domain bacteria includes 23 types, of which the following are of medical importance.
Most gram-negative bacteria are grouped into a phylum Proteobacteria(named after the Greek god Proteus, able to take on different forms). Type of Proteobacteria subdivided into 5 classes:
Class Alphaproteobacteria(birth Rickettsia, Orientia, Erlichia, Bartonella, Brucella);
Class Betaproteobacteria(birth Bordetella, Burholderia, Neisseria, Spirillum);
Class Gammaproteobacteria(members of the family enterobacteriaceae, childbirth Francisella, Legionella, Coxiella, Pseudomonas, Vibrio);
Class Deltaproteobacteria(genus Bilophila);
Class Epsilonproteobacteria(birth Campylobacter, Helicobacter). Gram-negative bacteria are also included in the following types:
type of Chlamydiae(birth Chlamydia, Chlamydophila) type of Spirochaetes(birth Spirocheta, Borrelia, Treponema, Leptospira); type of Bacteroides(birth Bacteroides, Prevotella, Porphyromonas).
Gram-positive bacteria come in the following types:
Type of Firmicutes includes class Clostridium(birth Clostridium, Peptococcus), Class Bacilli (Listeria, Staphylococcus, Lactobacillus, Streptococcus) and class Mollicutes(birth Mycoplasma, Ureaplasma), which are bacteria that do not have a cell wall;
type of Actinobacteria(birth Actinomyces, Micrococcus, Corynebacterium, Mycobacterium, Gardnerella, Bifidobacterium, Propionibacterium, Mobiluncus).
2.2.1. Morphological forms of bacteria
There are several basic forms of bacteria: coccoid, rod-shaped, convoluted and branching (Fig. 2.1).
Spherical shapes, or cocci- spherical bacteria 0.5-1 microns in size, which are divided by mutual arrangement into micrococci, diplococci, streptococci, tetracocci, sarcins and staphylococci.
Micrococci (from the Greek. micros- small) - separately located cells.
Diplococci (from the Greek. diploos- double), or paired cocci, arranged in pairs (pneumococcus, gonococcus, meningococcus), since the cells do not diverge after division. Pneumococcus (the causative agent of pneumonia) has a lanceolate shape on opposite sides, and gonococcus (the causative agent of gonorrhea) and meningococcus (causative agent)
Rice. 2.1. Shapes of bacteria
cause of epidemic meningitis) are shaped like coffee beans with their concave surfaces facing each other.
Streptococci (from the Greek. streptos- chain) - cells of a rounded or elongated shape that make up a chain due to cell division in the same plane and maintaining the connection between them at the place of division.
Sarcins (from lat. Sarcina- bundle, bale) are arranged in the form of packages of 8 cocci or more, since they are formed during cell division in three mutually perpendicular planes.
Staphylococci (from the Greek. staphyle- bunch of grapes) - cocci arranged in the form of a bunch of grapes as a result of division in different planes.
rod-shaped bacteria differ in size, shape of the ends of the cell and the relative position of the cells. Cell length 1-10 µm, thickness 0.5-2 µm. Sticks can be right
(E. coli, etc.) and irregular club-shaped (corynebacteria, etc.) forms. Rickettsiae are among the smallest rod-shaped bacteria.
The ends of the sticks can be, as it were, cut off (anthrax bacillus), rounded (E. coli), pointed (fusobacteria) or in the form of a thickening. In the latter case, the stick looks like a mace (Corynebacterium diphtheria).
The slightly curved rods are called vibrios (Vibrio cholerae). Most rod-shaped bacteria are arranged randomly, because after division, the cells diverge. If after division the cells remain connected by common fragments of the cell wall and do not diverge, then they are located at an angle to each other (corynebacterium diphtheria) or form a chain (anthrax bacillus).
Convoluted forms- spiral-shaped bacteria, which are of two types: spirilla and spirochetes. Spirilla have the appearance of corkscrew-shaped convoluted cells with large curls. Pathogenic spirillae include the causative agent of sodoku (rat bite disease), as well as campylobacter and helicobacteria, which have curves resembling the wings of a flying gull. Spirochetes are thin, long, convoluted bacteria that differ from spirilla in smaller curls and in the nature of movement. Their structure is described below.
branching - rod-shaped bacteria, which may have a Y-shaped branching, found in bifidobacteria, can also be presented as filamentous branched cells that can intertwine to form a mycelium, which is observed in actinomycetes.
2.2.2. Structure of a bacterial cell
The structure of bacteria is well studied using electron microscopy of whole cells and their ultrathin sections, as well as other methods. A bacterial cell is surrounded by a membrane consisting of a cell wall and a cytoplasmic membrane. Under the shell is protoplasm, consisting of cytoplasm with inclusions and a hereditary apparatus - an analogue of the nucleus, called the nucleoid (Fig. 2.2). There are additional structures: capsule, microcapsule, mucus, flagella, pili. Some bacteria under adverse conditions are able to form spores.
Rice. 2.2. Structure of a bacterial cell: 1 - capsule; 2 - cell wall; 3 - cytoplasmic membrane; 4 - mesosomes; 5 - nucleoid; 6 - plasmid; 7 - ribosomes; 8 - inclusions; 9 - flagellum; 10 - drank (villi)
cell wall- a strong, elastic structure that gives the bacteria a certain shape and, together with the underlying cytoplasmic membrane, restrains high osmotic pressure in the bacterial cell. It is involved in the process of cell division and transport of metabolites, has receptors for bacteriophages, bacteriocins and various substances. The thickest cell wall in gram-positive bacteria (Fig. 2.3). So, if the thickness of the cell wall of gram-negative bacteria is about 15-20 nm, then in gram-positive bacteria it can reach 50 nm or more.
The cell wall of bacteria is made up of peptidoglycan. Peptidoglycan is a polymer. It is represented by parallel polysaccharide glycan chains, consisting of repeating residues of N-acetylglucosamine and N-acetylmuramic acid connected by a glycosidic bond. This bond is broken by lysozyme, which is acetylmuramidase.
A tetrapeptide is attached to N-acetylmuramic acid by covalent bonds. The tetrapeptide consists of L-alanine, which is linked to N-acetylmuramic acid; D-glutamine, which in gram-positive bacteria is connected to L-lysine, and in gram-positive bacteria
Rice. 2.3. Scheme of the architectonics of the bacterial cell wall
bacteria - with diaminopimelic acid (DAP), which is a precursor of lysine in the process of bacterial biosynthesis of amino acids and is a unique compound found only in bacteria; The 4th amino acid is D-alanine (Fig. 2.4).
The cell wall of gram-positive bacteria contains a small amount of polysaccharides, lipids and proteins. The main component of the cell wall of these bacteria is a multilayer peptidoglycan (murein, mucopeptide), which makes up 40-90% of the mass of the cell wall. Tetrapeptides of different layers of peptidoglycan in gram-positive bacteria are connected to each other by polypeptide chains of 5 glycine (pentaglycine) residues, which gives the peptidoglycan a rigid geometric structure (Fig. 2.4, b). Covalently bound to the peptidoglycan of the cell wall of Gram-positive bacteria teichoic acids(from Greek. tekhos- wall), the molecules of which are chains of 8-50 residues of glycerol and ribitol connected by phosphate bridges. The shape and strength of the bacteria is given by the rigid fibrous structure of the multilayer, with cross-linked peptide cross-links of peptidoglycan.
Rice. 2.4. Structure of peptidoglycan: a - Gram-negative bacteria; b - gram-positive bacteria
The ability of gram-positive bacteria to retain gentian violet in combination with iodine (blue-violet color of bacteria) during Gram staining is associated with the property of multilayer peptidoglycan to interact with the dye. In addition, the subsequent treatment of a smear of bacteria with alcohol causes a narrowing of the pores in peptidoglycan and thereby retains the dye in the cell wall.
Gram-negative bacteria after exposure to alcohol lose the dye, which is due to a smaller amount of peptidoglycan (5-10% of the mass of the cell wall); they are discolored with alcohol, and when treated with fuchsin or safranin, they become red. This is due to the structural features of the cell wall. Peptidoglycan in the cell wall of gram-negative bacteria is represented by 1-2 layers. The tetrapeptides of the layers are interconnected by a direct peptide bond between the amino group of DAP of one tetrapeptide and the carboxyl group of D-alanine of the tetrapeptide of another layer (Fig. 2.4, a). Outside of peptidoglycan is a layer lipoprotein, bound to peptidoglycan via DAP. It is followed by outer membrane cell wall.
outer membrane is a mosaic structure represented by lipopolysaccharides (LPS), phospholipids and proteins. Its inner layer is represented by phospholipids, and LPS is located in the outer layer (Fig. 2.5). Thus, the outer mem-
Rice. 2.5. Structure of lipopolysaccharide
the brane is asymmetric. The LPS of the outer membrane consists of three fragments:
Lipid A - a conservative structure, almost the same in gram-negative bacteria. Lipid A consists of phosphorylated glucosamine disaccharide units to which long chains of fatty acids are attached (see Figure 2.5);
The core, or rod, of the cow part (from lat. core- core), relatively conservative oligosaccharide structure;
A highly variable O-specific polysaccharide chain formed by repeating identical oligosaccharide sequences.
LPS is anchored in the outer membrane by lipid A, which determines the toxicity of LPS and is therefore identified with endotoxin. The destruction of bacteria by antibiotics leads to the release of large amounts of endotoxin, which can cause endotoxic shock in the patient. From lipid A, the core, or the core part of the LPS, departs. The most constant part of the core of LPS is ketodeoxyoctonic acid. O-specific polysaccharide chain extending from the core part of the LPS molecule,
consisting of repeating oligosaccharide units, determines the serogroup, serovar (a type of bacteria detected using immune serum) of a certain strain of bacteria. Thus, the concept of LPS is associated with ideas about the O-antigen, according to which bacteria can be differentiated. Genetic changes can lead to defects, shortening of the bacterial LPS, and as a result, the appearance of rough colonies of R-forms that lose their O-antigen specificity.
Not all Gram-negative bacteria have a complete O-specific polysaccharide chain consisting of repeating oligosaccharide units. In particular, bacteria of the genus Neisseria have a short glycolipid called lipooligosaccharide (LOS). It is comparable to the R-form, which has lost O-antigenic specificity, observed in mutant rough strains. E. coli. The structure of the VOC resembles that of the human cytoplasmic membrane glycosphingolipid, so the VOC mimics the microbe, allowing it to evade the host's immune response.
The proteins of the matrix of the outer membrane permeate it in such a way that the protein molecules, called porins, they border hydrophilic pores through which water and small hydrophilic molecules with a relative mass of up to 700 D pass.
Between the outer and cytoplasmic membranes is periplasmic space, or periplasm containing enzymes (proteases, lipases, phosphatases, nucleases, β-lactamases), as well as components of transport systems.
In case of violation of the synthesis of the bacterial cell wall under the influence of lysozyme, penicillin, protective factors of the body and other compounds, cells with an altered (often spherical) shape are formed: protoplasts- bacteria completely devoid of a cell wall; spheroplasts Bacteria with a partially preserved cell wall. After removal of the cell wall inhibitor, such altered bacteria can reverse, i. acquire a full-fledged cell wall and restore its original shape.
Bacteria of the spheroid or protoplast type that have lost the ability to synthesize peptidoglycan under the influence of antibiotics or other factors and are able to multiply are called L-shaped(from the name of the D. Lister Institute, where they first
you have been studied). L-forms can also arise as a result of mutations. They are osmotically sensitive, spherical, flask-shaped cells of various sizes, including those passing through bacterial filters. Some L-forms (unstable) when the factor that led to changes in the bacteria is removed, can reverse, returning to the original bacterial cell. L-forms can form many pathogens of infectious diseases.
cytoplasmic membrane under electron microscopy of ultrathin sections, it is a three-layer membrane (2 dark layers 2.5 nm thick each are separated by a light one - intermediate). In structure, it is similar to the plasmolemma of animal cells and consists of a double layer of lipids, mainly phospholipids, with embedded surface and integral proteins, as if penetrating through the membrane structure. Some of them are permeases involved in the transport of substances. Unlike eukaryotic cells, there are no sterols in the cytoplasmic membrane of a bacterial cell (with the exception of mycoplasmas).
The cytoplasmic membrane is a dynamic structure with mobile components, therefore it is presented as a mobile fluid structure. It surrounds the outer part of the cytoplasm of bacteria and is involved in the regulation of osmotic pressure, transport of substances and energy metabolism of the cell (due to the enzymes of the electron transport chain, adenosine triphosphatase - ATPase, etc.). With excessive growth (compared to the growth of the cell wall), the cytoplasmic membrane forms invaginates - invaginations in the form of complexly twisted membrane structures, called mesosomes. Less complex twisted structures are called intracytoplasmic membranes. The role of mesosomes and intracytoplasmic membranes has not been fully elucidated. It is even suggested that they are an artifact that occurs after the preparation (fixation) of the preparation for electron microscopy. Nevertheless, it is believed that derivatives of the cytoplasmic membrane are involved in cell division, providing energy for the synthesis of the cell wall, take part in the secretion of substances, spore formation, i.e. in processes with high energy consumption. The cytoplasm occupies the bulk of the bacterial
ali cells and consists of soluble proteins, ribonucleic acids, inclusions and numerous small granules - ribosomes responsible for the synthesis (translation) of proteins.
Ribosomes bacteria have a size of about 20 nm and a sedimentation coefficient of 70S, in contrast to the 80S ribosomes characteristic of eukaryotic cells. Therefore, some antibiotics bind to bacterial ribosomes and inhibit bacterial protein synthesis without affecting protein synthesis in eukaryotic cells. Bacterial ribosomes can dissociate into two subunits: 50S and 30S. rRNA - conservative elements of bacteria ("molecular clock" of evolution). 16S rRNA is part of the small subunit of ribosomes, and 23S rRNA is part of the large subunit of ribosomes. The study of 16S rRNA is the basis of gene systematics, making it possible to assess the degree of relatedness of organisms.
In the cytoplasm there are various inclusions in the form of glycogen granules, polysaccharides, β-hydroxybutyric acid and polyphosphates (volutin). They accumulate with an excess of nutrients in the environment and serve as reserve substances for nutrition and energy needs.
Volyutin has an affinity for basic dyes and is easily detected using special staining methods (for example, according to Neisser) in the form of metachromatic granules. Toluidine blue or methylene blue stains volutin red-violet, and the bacterial cytoplasm blue. The characteristic arrangement of volutin granules is revealed in diphtheria bacillus in the form of intensely stained poles of the cell. Metachromatic staining of volutin is associated with a high content of polymerized inorganic polyphosphate. Under electron microscopy, they look like electron-dense granules 0.1–1 µm in size.
Nucleoid is the equivalent of the nucleus in bacteria. It is located in the central zone of bacteria in the form of double-stranded DNA, tightly packed like a ball. The bacterial nucleoid, unlike eukaryotes, does not have a nuclear envelope, nucleolus, and basic proteins (histones). Most bacteria contain one chromosome, represented by a DNA molecule closed in a ring. But some bacteria have two ring-shaped chromosomes. (V. cholerae) and linear chromosomes (see section 5.1.1). The nucleoid is detected under a light microscope after staining with specific DNA
methods: according to Felgen or according to Romanovsky-Giemsa. On electron diffraction patterns of ultrathin sections of bacteria, the nucleoid has the form of light zones with fibrillar, thread-like structures of DNA associated with certain areas with the cytoplasmic membrane or mesosome involved in chromosome replication.
In addition to the nucleoid, the bacterial cell contains extrachromosomal factors of heredity - plasmids (see section 5.1.2), which are covalently closed DNA rings.
Capsule, microcapsule, mucus.Capsule - a mucous structure more than 0.2 microns thick, firmly associated with the bacterial cell wall and having clearly defined outer boundaries. The capsule is distinguishable in smears-imprints from pathological material. In pure cultures of bacteria, the capsule is formed less frequently. It is detected by special methods of smear staining according to Burri-Gins, which create a negative contrast of the capsule substances: the ink creates a dark background around the capsule. The capsule consists of polysaccharides (exopolysaccharides), sometimes polypeptides, for example, in the anthrax bacillus, it consists of polymers of D-glutamic acid. The capsule is hydrophilic, contains a large amount of water. It prevents phagocytosis of bacteria. The capsule is antigenic: antibodies to the capsule cause its increase (capsule swelling reaction).
Many bacteria form microcapsule- mucous formation with a thickness of less than 0.2 microns, detected only with electron microscopy.
To be distinguished from a capsule slime - mucoid exopolysaccharides that do not have clear external boundaries. Slime is soluble in water.
Mucoid exopolysaccharides are characteristic of mucoid strains of Pseudomonas aeruginosa, often found in the sputum of patients with cystic fibrosis. Bacterial exopolysaccharides are involved in adhesion (sticking to substrates); they are also called glycocalyx.
The capsule and mucus protect bacteria from damage and drying out, since, being hydrophilic, they bind water well and prevent the action of protective factors of the macroorganism and bacteriophages.
Flagella bacteria determine the mobility of the bacterial cell. Flagella are thin filaments that take on
originating from the cytoplasmic membrane, are longer than the cell itself. The flagella are 12–20 nm thick and 3–15 µm long. They consist of three parts: a spiral thread, a hook and a basal body containing a rod with special disks (one pair of disks in gram-positive and two pairs in gram-negative bacteria). The discs of the flagella are attached to the cytoplasmic membrane and cell wall. This creates the effect of an electric motor with a rod - a rotor that rotates the flagellum. The difference of proton potentials on the cytoplasmic membrane is used as an energy source. The rotation mechanism is provided by proton ATP synthetase. The speed of rotation of the flagellum can reach 100 rpm. If a bacterium has several flagella, they begin to rotate synchronously, intertwining into a single bundle, forming a kind of propeller.
Flagella are made up of a protein called flagellin. (flagellum- flagellum), which is an antigen - the so-called H-antigen. Flagellin subunits are coiled.
The number of flagella in bacteria different types varies from one (monotrich) in Vibrio cholerae to ten or hundreds extending along the perimeter of the bacterium (peritrich), in Escherichia coli, Proteus, etc. Lofotrichs have a bundle of flagella at one end of the cell. Amphitrichous have one flagellum or a bundle of flagella at opposite ends of the cell.
Flagella are detected using electron microscopy of preparations sprayed with heavy metals, or in a light microscope after processing by special methods based on etching and adsorption of various substances, leading to an increase in the thickness of the flagella (for example, after silvering).
Villi, or pili (fimbriae)- filamentous formations, thinner and shorter (3-10 nm * 0.3-10 microns) than flagella. Pili extend from the cell surface and are composed of the pilin protein. Several types of saws are known. Pili of a general type are responsible for attachment to the substrate, nutrition and water-salt metabolism. They are numerous - several hundred per cell. Sex pili (1-3 per cell) create contact between cells, transferring genetic information between them by conjugation (see Chapter 5). Of particular interest are type IV pili, in which the ends are hydrophobic, as a result of which they twist, these pili are also called curls. Located-
they are located at the poles of the cell. These pili are found in pathogenic bacteria. They have antigenic properties, make contact between the bacterium and the host cell, and participate in the formation of a biofilm (see Chapter 3). Many pili are receptors for bacteriophages.
Disputes - a peculiar form of resting bacteria with a gram-positive type of cell wall structure. spore-forming bacteria of the genus bacillus, in which the size of the spore does not exceed the diameter of the cell, are called bacilli. Spore-forming bacteria in which the size of the spore exceeds the diameter of the cell, which is why they take the form of a spindle, are called clostridia, such as bacteria of the genus Clostridium(from lat. Clostridium- spindle). The spores are acid-resistant, therefore they are stained red according to the Aujeszky method or according to the Ziehl-Nelsen method, and the vegetative cell is blue.
Sporulation, the shape and location of spores in a cell (vegetative) are a species property of bacteria, which makes it possible to distinguish them from each other. The shape of the spores is oval and spherical, the location in the cell is terminal, i.e. at the end of the stick (in the causative agent of tetanus), subterminal - closer to the end of the stick (in pathogens of botulism, gas gangrene) and central (in anthrax bacilli).
The process of sporulation (sporulation) goes through a series of stages, during which part of the cytoplasm and the chromosome of a bacterial vegetative cell are separated, surrounded by a growing cytoplasmic membrane, and a prospore is formed.
The prospore protoplast contains a nucleoid, a protein-synthesizing system, and an energy-producing system based on glycolysis. Cytochromes are absent even in aerobes. Does not contain ATP, energy for germination is stored in the form of 3-glycerol phosphate.
The prospore is surrounded by two cytoplasmic membranes. The layer that surrounds the inner membrane of the spore is called spore wall, it consists of peptidoglycan and is the main source of the cell wall during spore germination.
Between the outer membrane and the spore wall, a thick layer is formed, consisting of peptidoglycan, which has many crosslinks, - cortex.
Outside of the outer cytoplasmic membrane is located spore shell, consisting of keratin-like proteins,
containing multiple intramolecular disulfide bonds. This shell provides resistance to chemical agents. Spores of some bacteria have an additional cover - exosporium lipoprotein nature. Thus, a multilayer poorly permeable shell is formed.
Sporulation is accompanied by intensive consumption by the prospore, and then by the emerging spore shell of dipicolinic acid and calcium ions. The spore acquires heat resistance, which is associated with the presence of calcium dipicolinate in it.
The spore can persist for a long time due to the presence of a multi-layered shell, calcium dipicolinate, low water content and sluggish metabolic processes. In the soil, for example, anthrax and tetanus pathogens can persist for decades.
Under favorable conditions, spores germinate through three successive stages: activation, initiation, growth. In this case, one bacterium is formed from one spore. Activation is the readiness for germination. At a temperature of 60-80 °C, the spore is activated for germination. Germination initiation takes several minutes. The growth stage is characterized by rapid growth, accompanied by the destruction of the shell and the release of the seedling.
2.2.3. Features of the structure of spirochetes, rickettsiae, chlamydia, actinomycetes and mycoplasmas
Spirochetes- thin long convoluted bacteria. They consist of an outer membranous cell wall that surrounds the cytoplasmic cylinder. On top of the outer membrane is a transparent sheath of glycosaminoglycan nature. Under the outer membrane cell wall, fibrils are located, twisting around the cytoplasmic cylinder, giving the bacteria a helical shape. Fibrils are attached to the ends of the cell and directed towards each other. The number and arrangement of fibrils varies in different species. Fibrils are involved in the movement of spirochetes, giving the cells rotational, flexion and translational motion. In this case, spirochetes form loops, curls, bends, which are called secondary curls. Spirochetes do not perceive dyes well. Usually they are stained according to Romanovsky-Giemsa or silvered. Live
the form of a spirochete is examined using phase-contrast or dark-field microscopy.
Spirochetes are represented by three genera pathogenic to humans: Treponema, Borrelia, Leptospira.
Treponema(genus Treponema) have the appearance of thin corkscrew-twisted threads with 8-12 uniform small curls. There are 3-4 fibrils (flagella) around the treponema protoplast. The cytoplasm contains cytoplasmic filaments. Pathogenic representatives are T. pallidum- causative agent of syphilis T.pertenue- the causative agent of a tropical disease - yaws. There are also saprophytes - inhabitants of the human oral cavity, silt of reservoirs.
Borrelia(genus Borrelia, unlike treponemas, they are longer, have 3-8 large curls and 7-20 fibrils. These include the causative agent of relapsing fever (B. recurrentis) and the causative agents of Lyme disease (B. burgdorferi) and other diseases.
Leptospira(genus Leptospira) have curls shallow and frequent in the form of a twisted rope. The ends of these spirochetes are curved like hooks with thickenings at the ends. Forming secondary curls, they take the form of the letters S or C; have two axial fibrils. Pathogenic representative L. interrogans causes leptospirosis when ingested with water or food, leading to hemorrhages and jaundice.
Rickettsia have a metabolism independent of the host cell, however, they may receive macroergic compounds from the host cell for their reproduction. In smears and tissues, they are stained according to Romanovsky-Giemsa, according to Machiavello-Zdrodovsky (rickettsia are red, and infected cells are blue).
Rickettsia causes epidemic typhus in humans. (R. prowazekii), tick-borne rickettsiosis (R. sibirica), Rocky Mountain spotted fever (R. rickettsii) and other rickettsiosis.
The structure of their cell wall resembles that of gram-negative bacteria, although there are differences. It does not contain typical peptidoglycan: N-acetylmuramic acid is completely absent in its composition. The cell wall consists of a double outer membrane, which includes lipopolysaccharide and proteins. Despite the absence of peptidoglycan, the chlamydia cell wall is rigid. The cytoplasm of the cell is limited by the inner cytoplasmic membrane.
The main method for detecting chlamydia is the Romanovsky-Giemsa stain. The color of the stain depends on the stage of the life cycle: elementary bodies turn purple against the background of the blue cytoplasm of the cell, reticular bodies turn blue.
In humans, chlamydia causes damage to the eyes (trachoma, conjunctivitis), urogenital tract, lungs, etc.
actinomycetes- branching, filamentous or rod-shaped gram-positive bacteria. Its name (from the Greek. actis- Ray, mykes- fungus) they received in connection with the formation of drusen in the affected tissues - granules of tightly interwoven threads in the form
rays extending from the center and ending in flask-shaped thickenings. Actinomycetes, like fungi, form mycelium - filamentous intertwining cells (hyphae). They form substrate mycelium, which is formed as a result of cells growing into the nutrient medium, and air, growing on the surface of the medium. Actinomycetes can divide by fragmenting the mycelium into cells similar to rod-shaped and coccoid bacteria. On aerial hyphae of actinomycetes, spores are formed that serve for reproduction. Actinomycete spores are usually not heat resistant.
A common phylogenetic branch with actinomycetes is formed by the so-called nocardio-like (nocardioform) actinomycetes - a collective group of irregularly shaped rod-shaped bacteria. Their individual representatives form branching forms. These include bacteria of the genera Corynebacterium, Mycobacterium, Nocardia and others. Nocardioid actinomycetes are distinguished by the presence in the cell wall of the sugars of arabinose, galactose, as well as mycolic acids and large amounts of fatty acids. Mycolic acids and cell wall lipids determine the acid resistance of bacteria, in particular Mycobacterium tuberculosis and leprosy (when stained according to Ziehl-Nelsen, they are red, and non-acid-resistant bacteria and tissue elements, sputum are blue).
Pathogenic actinomycetes cause actinomycosis, nocardia - nocardiosis, mycobacteria - tuberculosis and leprosy, corynebacteria - diphtheria. Saprophytic forms of actinomycetes and nocardia-like actinomycetes are widespread in the soil, many of them are producers of antibiotics.
Mycoplasmas- small bacteria (0.15-1 µm) surrounded only by a cytoplasmic membrane containing sterols. They belong to the class Mollicutes. Due to the lack of a cell wall, mycoplasmas are osmotically sensitive. They have a variety of shapes: coccoid, filiform, flask-shaped. These forms are visible on phase-contrast microscopy of pure cultures of mycoplasmas. On a dense nutrient medium, mycoplasmas form colonies resembling fried eggs: a central opaque part immersed in the medium and a translucent periphery in the form of a circle.
Mycoplasmas cause SARS in humans (Mycoplasma pneumoniae) and lesions of the urinary tract
(M. hominis and etc.). Mycoplasmas cause diseases not only in animals but also in plants. Non-pathogenic representatives are quite widespread.
2.3. The structure and classification of mushrooms
Mushrooms belong to the domain eukarya, kingdom Fungi (Mycota, Mycetes). Fungi and protozoa have recently been divided into independent kingdoms: the kingdom Eumycota(true mushrooms), kingdom Chromista and kingdom Protozoa. Some microorganisms previously thought to be fungi or protozoa have been moved to a new kingdom Chromista(chromes). Mushrooms are multicellular or unicellular non-photosynthetic (chlorophyll-free) eukaryotic microorganisms with a thick cell wall. They have a nucleus with a nuclear membrane, a cytoplasm with organelles, a cytoplasmic membrane, and a multilayered rigid cell wall consisting of several types of polysaccharides (mannans, glucans, cellulose, chitin), as well as protein, lipids, etc. Some fungi form a capsule. The cytoplasmic membrane contains glycoproteins, phospholipids and ergosterols (in contrast to cholesterol, the main sterol of mammalian tissues). Most fungi are obligate or facultative aerobes.
Fungi are widely distributed in nature, especially in the soil. Some mushrooms contribute to the production of bread, cheese, dairy products and alcohol. Other fungi produce antimicrobial antibiotics (eg penicillin) and immunosuppressive drugs (eg cyclosporine). Fungi are used by geneticists and molecular biologists to model various processes. Phytopathogenic fungi cause significant damage to agriculture, causing fungal diseases of cereal plants and grain. Infections caused by fungi are called mycoses. There are hyphae and yeast fungi.
Hyphal (mold) fungi, or hyphomycetes, consist of thin threads 2-50 microns thick, called hyphae, which are woven into a mycelium or mycelium (mold). The body of the fungus is called the thallus. Distinguish demacia (pigmented - brown or black) and hyaline (non-pigmented) hyphomycetes. Hyphae growing into the nutrient substrate are responsible for the nutrition of the fungus and are called vegetative hyphae. Hyphae, ra-
growing above the surface of the substrate are called aerial or reproductive hyphae (responsible for reproduction). Colonies due to aerial mycelium have a fluffy appearance.
There are lower and higher fungi: the hyphae of higher fungi are separated by partitions, or septa with holes. The hyphae of lower fungi do not have partitions, representing multinucleated cells called coenocytic (from the Greek. koenos- single, general).
Yeast fungi (yeast) are mainly represented by individual oval cells with a diameter of 3-15 microns, and their colonies, unlike hyphal fungi, have a compact appearance. According to the type of sexual reproduction, they are distributed among higher fungi - ascomycete and basidiomycete. During asexual reproduction, yeasts form buds or divide. They can form pseudohyphae and false mycelium (pseudomycelium) in the form of chains of elongated cells - "wieners". Mushrooms that are similar to yeast but do not reproduce sexually are called yeast-like. They reproduce only asexually - by budding or division. The concepts of "yeast-like fungi" are often identified with the concept of "yeast".
Many fungi have dimorphism - the ability to hyphal (mycelial) or yeast-like growth, depending on the cultivation conditions. In an infected organism, they grow as yeast-like cells (yeast phase), and form hyphae and mycelium on nutrient media. Dimorphism is associated with a temperature factor: at room temperature, mycelium is formed, and at 37 ° C (at human body temperature), yeast-like cells are formed.
Fungi reproduce either sexually or asexually. sexual reproduction fungi occurs with the formation of gametes, sexual spores and other sexual forms. Sexual forms are called teleomorphs.
Asexual reproduction of fungi occurs with the formation of the corresponding forms, called anamorphs. Such reproduction occurs by budding, fragmentation of hyphae and asexual spores. Endogenous spores (sporangiospores) mature inside a rounded structure - sporangium. Exogenous spores (conidia) are formed at the tips of fruiting hyphae, the so-called conidiophores.
There are various conidia. Arthroconidia (arthrospores), or talloconidia, are formed with uniform septation and dissection of hyphae, and blastoconidia are formed as a result of budding. Small unicellular conidia are called microconidia, large multicellular conidia are called macroconidia. The asexual forms of fungi also include chlamydoconidia, or chlamydospores (thick-walled large resting cells or a complex of small cells).
There are perfect and imperfect mushrooms. Perfect mushrooms have a sexual mode of reproduction; they include zygomycetes (Zygomycota), ascomycetes (Ascomycota) and basidiomycetes (Basidiomycota). Imperfect fungi have only asexual reproduction; these include a formal conditional type / group of fungi - deuteromycetes (Deiteromycota).
Zygomycetes belong to the lower fungi (non-septate mycelium). They include members of the genus Mucor, Rhizopus, Rhizomucor, Absidia, Basidiobolus, Conidiobolus. Distributed in soil and air. They can cause zygomycosis (mucormycosis) of the lungs, brain and other human organs.
During asexual reproduction of zygomycetes on a fruiting hypha (sporangiophore), a sporangium is formed - a spherical thickening with a shell containing numerous sporangiospores (Fig. 2.6, 2.7). Sexual reproduction in zygomycetes occurs with the help of zygospores.
Ascomycetes (marsupials) have septate mycelium (except for unicellular yeasts). They got their name from the main fruiting organ - the bag, or ascus, containing 4 or 8 haploid sexual spores (ascospores).
Ascomycetes include individual representatives (teleomorphs) of the genera Aspergillus and Penicillium. Most mushroom genera Aspergillus, Penicillium are anamorphs, i.e. breed only harmlessly
Rice. 2.6. Mushrooms of the genus Mucor(Fig. A.S. Bykov)
Rice. 2.7. Mushrooms of the genus Rhizopus. Development of sporangia, sporangiospores and rhizoids
in a lym way with the help of asexual spores - conidia (Fig. 2.8, 2.9) and should be classified according to this feature as imperfect fungi. In fungi of the genus Aspergillus at the ends of fruit-bearing hyphae, conidiophores, there are thickenings - sterigmas, phialides, on which chains of conidia are formed ("lech mold").
In fungi of the genus Penicillium(racus) the fruiting hypha resembles a brush, since thickenings are formed from it (on the conidiophore), branching into smaller structures - sterigmas, phialides, on which there are chains of conidia. Some types of aspergillus can cause aspergillosis and aflatoxicosis, penicillium can cause penicilliosis.
Representatives of ascomycetes are teleomorphs of the genera Trichophyton, Microsporum, Histoplasma, Blastomyces, as well as trembling
Rice. 2.8. Mushrooms of the genus Penicillium. Chains of conidia extend from the phialides
Rice. 2.9. Mushrooms of the genus Aspergillus fumigatus. Chains of conidia extend from the phialides
Basidiomycetes include cap mushrooms. They have a septate mycelium and form sexual spores - basidiospores by lacing off from the basidium - the end cell of the mycelium, homologous to the ascus. Some yeasts, such as teleomorphs, are basidiomycetes. Cryptococcus neoformans.
Deuteromycetes are imperfect fungi (Fungi imperfecti, anamorphic fungi, conidial fungi). This is a conditional, formal taxon of fungi, uniting fungi that do not have sexual reproduction. Recently, instead of the term "deuteromycetes", the term "mitosporous fungi" has been proposed - fungi that reproduce by asexual spores, i.e. by mitosis. When establishing the fact of sexual reproduction of imperfect fungi, they are transferred to one of the known types - Ascomycota or Basidiomycota, giving the name of the teleomorphic form. Deuteromycetes have septate mycelium and reproduce only by asexual formation of conidia. Deuteromycetes include imperfect yeasts (yeast-like fungi), for example, some fungi of the genus Candida affecting the skin, mucous membranes and internal organs (candidiasis). They are oval in shape, 2-5 microns in diameter, divide by budding, form pseudohyphae (pseudomycelium) in the form of chains of elongated cells, sometimes form hyphae. For candida albicans the formation of chlamydospores is characteristic (Fig. 2.10). Deuteromycetes also include other fungi that do not have a sexual mode of reproduction, related to genera Epidermophyton, Coccidioides, Paracoccidioides, Sporothrix, Aspergillus, Phialophora, Fonsecaea, Exophiala, Cladophialophora, Bipolaris, Exerohilum, Wangiella, Alrernaria and etc.
Rice. 2.10. Mushrooms of the genus candida albicans(Fig. A.S. Bykov)
2.4. Structure and classification of protozoa
The simplest belong to the domain eukarya, animal kingdom (Animalia) sub-kingdom Protozoa. Recently it has been proposed to single out protozoa to the rank of kingdom Protozoa.
The protozoan cell is surrounded by a membrane (pellicle) - an analogue of the cytoplasmic membrane of animal cells. It has a nucleus with a nuclear membrane and a nucleolus, a cytoplasm containing the endoplasmic reticulum, mitochondria, lysosomes and ribosomes. The sizes of protozoa range from 2 to 100 microns. When stained according to Romanovsky-Giemsa, the nucleus of the protozoa is red, and the cytoplasm is blue. Protozoa move with the help of flagella, cilia or pseudopodia, some of them have digestive and contractile (excretory) vacuoles. They can feed as a result of phagocytosis or the formation of special structures. By type of nutrition, they are divided into heterotrophs and autotrophs. Many protozoa (dysentery amoeba, Giardia, Trichomonas, Leishmania, Balantidia) can grow on nutrient media containing native proteins and amino acids. Cell cultures, chicken embryos and laboratory animals are also used for their cultivation.
The simplest reproduce asexually - by double or multiple (schizogony) division, and some also sexually (sporogony). Some protozoa reproduce extracellularly (Giardia), while others reproduce intracellularly (Plasmodium, Toxoplasma, Leishmania). The life cycle of protozoa is characterized by stages - the formation of the trophozoite stage and the cyst stage. Cysts are dormant stages resistant to changes in temperature and humidity. Cysts are acid resistant Sarcocystis, Cryptosporidium and Isospora.
Previously, the protozoa that cause disease in humans were represented by 4 types 1 ( Sarcomastigophora, Apicomplexa, Ciliophora, Microspora). These types have recently been reclassified to large quantity, new kingdoms appeared - Protozoa and Chromista(Table 2.2). To a new kingdom Chromista(chromovics) included some protozoa and fungi (blastocysts, oomycetes and Rhinosporidium seeberi). Kingdom Protozoa includes amoeba, flagellates, sporozoans and ciliates. They are divided into different types, among which there are amoeba, flagellates, sporozoans and ciliates.
Table 2.2. Kingdom representatives Protozoa and Chromista, of medical importance
1 type Sarcomastigophora consisted of subtypes Sarcodina and Mastigophora. Subtype Sarcodina(sarcode) included the dysenteric amoeba, and the subtype Mastigophora(flagellates) - trypanosomes, leishmania, giardia and Trichomonas. Type of Apicomplexa included class Sporozoa(sporozoa), which included malaria plasmodia, toxoplasma, cryptosporidium, etc. Type Ciliophora includes balantidia, and the type Microspora- microsporidia.
The end of the table. 2.2
Amoebas are the causative agent of human amoebiasis - amoebic dysentery (Entamoeba histolytica), free-living and non-pathogenic amoeba (intestinal amoeba, etc.). Amoebas reproduce binary asexually. Their life cycle consists of the trophozoite stage (growing, mobile cell, unstable) and the cyst stage. Trophozoites move with the help of pseudopodia, which capture and immerse nutrients into the cytoplasm. From
trophozoite, a cyst is formed that is resistant to external factors. Once in the intestine, it turns into a trophozoite.
Flagellates are characterized by the presence of flagella: Leishmania has one flagellum, Trichomonas has 4 free flagella and one flagellum connected to a short undulating membrane. They are:
Flagellates of blood and tissues (leishmania - causative agents of leishmaniasis; trypanosomes - causative agents of sleeping sickness and Chagas disease);
Intestinal flagellates (giardia - the causative agent of giardiasis);
Flagellates of the genitourinary tract (Trichomonas vaginalis - the causative agent of trichomoniasis).
Ciliated are represented by balantidia, which affect the human large intestine (balantidiasis dysentery). Balantidia have a trophozoite and a cyst stage. The trophozoite is mobile, has numerous cilia, thinner and shorter than the flagella.
2.5. The structure and classification of viruses
Viruses are the smallest microbes belonging to the kingdom Virae(from lat. virus- poison). They do not have a cellular structure and are
The structure of viruses, due to their small size, is studied using electron microscopy of both virions and their ultrathin sections. The size of viruses (virions) is determined directly using electron microscopy or indirectly by ultrafiltration through filters with a known pore diameter, by ultracentrifugation. The size of viruses ranges from 15 to 400 nm (1 nm is equal to 1/1000 microns): small viruses, the size of which is similar to the size of ribosomes, include parvoviruses and poliovirus, and the largest ones are variola virus (350 nm). Viruses differ in the form of virions, which have the form of rods (tobacco mosaic virus), bullets (rabies virus), spheres (polio viruses, HIV), filaments (filoviruses), sperm (many bacteriophages).
Viruses amaze the imagination with their variety of structure and properties. Unlike cellular genomes, which contain uniform double-stranded DNA, viral genomes are extremely diverse. There are DNA- and RNA-containing viruses that are haploid, i.e. have one set of genes. Only retroviruses have a diploid genome. The genome of viruses contains from 6 to 200 genes and is represented by various types nucleic acids: double-stranded, single-stranded, linear, circular, fragmented.
Among single-stranded RNA-containing viruses, genomic plus-strand RNA and minus-strand RNA (RNA polarity) are distinguished. Plus-thread (positive thread) of RNA of these viruses, in addition to the genomic (hereditary) function, performs the function of information, or matrix RNA (mRNA, or mRNA); it is a template for protein synthesis on the ribosomes of the infected cell. Plus-strand RNA is infectious: when introduced into sensitive cells, it can cause an infectious pro-
cess. The negative thread (negative thread) of RNA-containing viruses performs only a hereditary function; for protein synthesis, a complementary strand is synthesized on the negative strand of RNA. Some viruses have an ambipolar RNA genome. (Ambience from the Greek ambi- on both sides, double complementarity), i.e. contains plus and minus RNA segments.
A distinction is made between simple viruses (eg hepatitis A virus) and complex viruses (eg influenza, herpes, coronaviruses).
Simple, or non-enveloped, viruses have only nucleic acid associated with a protein structure called a capsid (from lat. capsa- case). The proteins associated with the nucleic acid are known as nucleoproteins, and the association of the viral capsid proteins of the virus with the viral nucleic acid is called the nucleocapsid. Some simple viruses can form crystals (eg foot-and-mouth disease virus).
The capsid includes repeating morphological subunits - capsomeres, composed of several polypeptides. The nucleic acid of the virion binds to the capsid to form the nucleocapsid. The capsid protects the nucleic acid from degradation. In simple viruses, the capsid is involved in attachment (adsorption) to the host cell. Simple viruses leave the cell as a result of its destruction (lysis).
Complex, or enveloped, viruses (Fig. 2.11), in addition to the capsid, have a membrane double lipoprotein shell (synonym: supercapsid, or peplos), which is acquired by budding the virion through the cell membrane, for example, through the plasma membrane, nuclear membrane or endoplasmic reticulum membrane. On the envelope of the virus are glycoprotein spikes,
or spines, ash meters. The destruction of the shell with ether and other solvents inactivates complex viruses. Under the shell of some viruses is a matrix protein (M-protein).
Virions have a helical, icosahedral (cubic) or complex type of capsid (nucleocapsid) symmetry. The helical type of symmetry is due to the helical structure of the nucleocapsid (for example, in influenza viruses, coronaviruses): capsomeres are stacked in a spiral along with the nucleic acid. The icosahedral type of symmetry is due to the formation of an isometric hollow body from a capsid containing a viral nucleic acid (for example, in the herpes virus).
The capsid and shell (supercapsid) protect virions from environmental influences, determine the selective interaction (adsorption) of their receptor proteins with a certain
Rice. 2.11. The structure of enveloped viruses with icosahedral (a) and helical (b) capsid
cells, as well as antigenic and immunogenic properties of virions.
The internal structures of viruses are called the core. In adenoviruses, the core consists of histone-like proteins associated with DNA; in reoviruses, it consists of proteins of the internal capsid.
Laureate Nobel Prize D. Baltimore proposed a Baltimore classification system based on the mechanism of mRNA synthesis. This classification places viruses in 7 groups (Table 2.3). International Committee on Taxonomy of Viruses (ICTV) adopted a universal classification system that uses taxonomic categories such as family (the name ends with viridae), subfamily (name ends with virinae), genus (name ends with virus). The type of virus has not received a binomial name, as in bacteria. Viruses are classified according to the type of nucleic acid (DNA or RNA), its structure and the number of strands. They have double-stranded or single-stranded nucleic acids; positive (+), negative (-) nucleic acid polarity or mixed nucleic acid polarity, ambipolar (+, -); linear or circular nucleic acid; fragmented or non-fragmented nucleic acid. The size and morphology of virions, the number of capsomeres and the type of symmetry of the nucleocapsid, the presence of a shell (supercapsid), sensitivity to ether and deoxycholate, the place of reproduction in the cell, antigenic properties, etc. are also taken into account.
Table 2.3. Major viruses of medical importance
Continuation of the table. 2.3
The end of the table. 2.3
Viruses infect animals, bacteria, fungi and plants. Being the main causative agents of human infectious diseases, viruses also participate in the processes of carcinogenesis, can be transmitted in various ways, including through the placenta (rubella virus, cytomegalovirus, etc.), affecting the human fetus. They can also lead to post-infectious complications - the development of myocarditis, pancreatitis, immunodeficiency, etc.
Non-cellular life forms, in addition to viruses, include prions and viroids. Viroids are small molecules of circular, supercoiled RNA that do not contain protein and cause diseases in plants. Pathological prions are infectious protein particles that cause special conformational diseases as a result of a change in the structure of the normal cellular prion protein ( PrP c), which is found in the body of animals and humans. PrP with performs regulatory functions. It is encoded by the normal prion gene (PrP gene) located on the short arm of the 20th human chromosome. Prion diseases proceed according to the type of transmissible spongiform encephalopathy (Crutzfeldt-Jakob disease, kuru, etc.). In this case, the prion protein acquires a different, infectious form, designated as PrP sc(sc from scrapie- scrapie - prion infection of sheep and goats). This infectious prion protein is fibril-like and differs from the normal prion protein in its tertiary or quaternary structure.
Tasks for self-training (self-control)
BUT. Name the microbes that are prokaryotes:
2. Viruses.
3. Bacteria.
4. Prions.
B. List the characteristics of a prokaryotic cell:
1. Ribosomes 70S.
2. The presence of peptidoglycan in the cell wall.
3. The presence of mitochondria.
4. Diploid set of genes.
AT. List the components of peptidoglycan:
1. Teichoic acids.
2. N-acetylglucosamine.
3. Lipopolysarid.
4. Tetrapeptide.
G. Note the structural features of the cell wall of Gram-negative bacteria:
1. Mesodiaminopimelic acid.
2. Teichoic acids.
4. Porin proteins.
D. Name the functions of spores in bacteria:
1. Save the view.
2. Heat resistance.
3. Settlement of the substrate.
4. Reproduction.
1. Rickettsia.
2. Actinomycetes.
3. Spirochetes.
4. Chlamydia.
AND. Name the features of actinomycetes:
1. They have heat-labile spores.
2. Gram-positive bacteria.
3. There is no cell wall.
4. Have a twisted shape.
Z. Name the features of spirochetes:
1. Gram-negative bacteria.
2. They have a motor fibrillar apparatus.
3. They have a twisted shape.
AND. Name the protozoa that have an apical complex that allows them to penetrate inside the cell:
1. Malarial Plasmodium.
3. Toxoplasma.
4. Cryptosporidium.
TO. name distinguishing feature complex viruses:
1. Two types of nucleic acid.
2. The presence of a lipid membrane.
3. Double capsid.
4. The presence of non-structural proteins. L. Mark the higher mushrooms:
1. Mucor.
2. Candida.
3. Penicillium.
4. Aspergillus.