Classification, or systematics of microorganisms (from the Greek Systematikos - ordered, systematized), is a branch of microbiology that deals with the creation of a classification of microorganisms based on their properties and family relationships. The term "taxonomy" is sometimes used as a synonym for the concept of "taxonomy of microorganisms".
Currently, there is no universal, only correct classification. Depending on the task, microorganisms can be classified by morphological features (rods, cocci, convoluted, etc.), by tinctorial features (gram-positive, gram-negative, etc.), by physiological features (thermophilic, psychrophilic, acidophilic, aerobic etc.), by ecological traits (nitrogen-fixing, nitrifying, sulfate-reducing, cellulose-destroying, etc.), by interspecific relationships (antagonists, synergists, commensals, etc.), by types of taxis, genotypic and phylogenetic characters. Microorganisms are also classified according to the degree of danger to humans, animals and environment. Thus, the classification of microorganisms is a subjective processing of objective characteristics.
Modern taxonomy of microorganisms includes three main areas:
1. Characterization of microorganisms- Obtaining all kinds of information about the properties and parameters necessary to assign the determined microorganisms to a particular taxon.
2. Classification or taxonomy, i.e. the process of ordering microorganisms into taxonomic groups based on similarity.
3. Nomenclature- assignment of scientific names to taxonomic groups (taxa).
The basic taxonomic unit in the taxonomy of microorganisms is view. According to general biological concepts, a species is a group of closely related organisms that have a common root of origin and at this stage of evolution are characterized by certain morphological, biochemical and physiological features, isolated by selection from other species and adapted to a specific habitat. An important species trait is the ability of organisms to interbreed and produce offspring.
The definition of a species in bacteria is fundamentally different from the classical definition species because they do not have sexual reproduction. According to modern concepts, closely related organisms, with a 70% level of DNA homology and similar in terms of morphological, biochemical, and physiological characteristics, are classified as one type of bacteria.
The following taxonomic categories are also used in the hierarchical classification of microorganisms: subspecies- a group of closely related similar organisms within kind with a level of DNA homology above 70%; genus- a taxonomic group that unites related species, and further - family, suborder, order, subclass, class, realm And domain(or supra-kingdom). Families and domains are now largely described, while other taxonomic groups are in the process of systematization.
Domains are the highest taxa of microorganisms, corresponding to previously identified kingdoms. According to the modern classification, the entire diversity of microorganisms is represented by three domains: Bacteria (prokaryotic microorganisms, true bacteria), Archaea (another evolutionary branch of prokaryotic microorganisms) and Eukarya (eukaryotic microorganisms)(Fig. 2). Of these, two domains (Bacteria and Archaea) include only representatives of prokaryotes, which are separated into a separate supra-kingdom - Procariolae.
Fig.2. Universal phylogenetic tree of living organisms.
The most accurate, informative, and user-friendly classification system is one in which taxa are defined based on a variety of consistent characteristics obtained using various modern methods. Such an approach to the selection of taxa is called polyphasic.
The main methods of modern polyphasic taxonomy are: genotypic, phenotypic and phylogenetic.
The genotypic method is dominant in polyphasic taxonomy. It is based on the study of the C+G composition of DNA, on the study of DNA-rRNA homology, on the establishment of related relationships between microorganisms that are encoded in the nucleotide sequences of the 16S or 23S r-RNA genes. For example, when determining the belonging of a microorganism to a certain species, the level of similarity of the DNA nucleotide sequences of about 70% plays a paramount role. Therefore, the genotypic method is often called the method of genomic fingerprinting.
Phenotypic studies are used most often in various schemes for the identification of microorganisms, for the formal description of a taxon, from variety and subspecies to genus and family. While genotypic data is necessary to place a taxon on a phylogenetic tree and in a classification system, phenotypic characterization provides descriptive information that allows identification of a particular microorganism species. Classical phenotypic characteristics include morphological, physiological, biochemical, chemotaxonomic and serological characteristics of microorganisms.
Morphological features indicate the size and shape of the microorganism (coccus, bacillus, spirilla), whether it has a capsule or spores, whether the cells are combined into chains, tetrads or packages, whether they have flagella and how they are located, whether the cells are stained according to Gram. The morphology of bacteria includes the study of cultural properties, i.e. the nature of growth on nutrient media, the shape of colonies on dense nutrient media, pigment formation.
Physiological features characterize the mechanism of metabolism, the method of obtaining energy, the ability of a given microorganism to transform certain substances, its relationship to carbon, nitrogen, oxygen, temperature, pH of the environment.
Biochemical signs are determined by the ability of microorganisms to decompose certain sugars, form hydrogen sulfide, ammonia and other compounds.
Chemotaxonomic features characterize the chemical composition of the cell cytoplasm. The taxonomic specificity of the composition of fatty acids, lipoproteins, lipopolysaccharides, pigments, polyamines, proteins and other chemical components of the cell is widely used in the classification of microorganisms.
Serological properties, or serotyping, are based on the detection of variability in the antigenic components of bacterial cells. Such components can be flagella, fimbriae. capsules, cell wall, enzymes and toxins. To identify the antigenic properties of a bacterial cell, various serological reactions are used: precipitation reaction, complement bonding reaction, precipitation, etc.
Thus, phenotypic characteristics are distinguished by a large volume and variety of information obtained, which is difficult to process manually. There was a need for a computer, numerical analysis of the data obtained. Numerical (numerical) taxonomy has appeared, which allows using computer programs analyze the phenotypic and genotypic characteristics of microorganisms. The use of numerical analysis in taxonomic practice is called "computer identification".
Phylogenetic methods (from the Greek phylon - genus, tribe and genesis - origin, occurrence) allow you to trace the process historical development microorganisms both in general and their individual taxonomic groups: species, subspecies, genera, families, suborders, orders, subclasses, classes, kingdoms and domains.
Phylogenetic relationships between microorganisms are studied by the methods of genomic fingerprinting, molecular biology, computer identification. Based on the obtained data, phylogenetic trees are built, which reflect the evolutionary relationships between microorganisms (Fig. 3). The created phylogenetic trees cannot be used to build a hierarchical classification of microorganisms and do not replace taxonomy. They are one of its elements.
Nomenclature- deals with issues of precise and uniform names. Ego is a system of names used in a certain field of knowledge. In accordance with international rules, taxonomic groups of microorganisms are assigned names.
Even before the introduction of the first rules of nomenclature, a huge number of microorganisms were described. Moreover, the same bacterium could be assigned to taxa with different names. To avoid this, the International Code of Nomenclature defined all the priority names of bacteria published since May 1, 1753. As a result, a "List of Recognized Names of Bacteria" was created, which came into force on January 1, 1980. Currently, the name of microorganisms is assigned in accordance with the rules of the International Code of Nomenclature for Bacteria. The competence of the Code extends only to the rules for assigning and using the scientific names of microorganisms. Classification issues are resolved regardless of the Code on the basis of ongoing taxonomic studies.
Rice. 3. Phylogenetic tree of bacteria.
In microbiology, as in biology, a double (binary) nomenclature, proposed as early as 1760 by Carl Linnaeus, is adopted to designate bacterial species.
The first word is the genus name. Usually this is a Latin word, it is written with capital letter and characterizes any morphological or physiological feature, or the name of the scientist who discovered this microbe. For example, the genus Pasteurella is named after the French scientist L. Pasteur, the American microbiologist Salmon - the genus Salmonella, the German scientist T. Escherich - the genus Escherichia, the Japanese microbiologist Shiga - the genus Shigella, the English bacteriologists D. Bruce and S. Erwin - the genera "Brucella" and "Ervinia", Russian scientists Kuznetsov and Lyambl - the genera "Kuznetsovia" and "Lamblia", etc. The genus name of a microorganism is usually abbreviated to one or two letters.
The second word denotes the specific epithet in the name of the microorganism and, as a rule, is a derivative of a noun that describes the color of the colony, the source of origin of the microorganism, the process or disease caused by it. The species name is capitalized and never abbreviated. For example, Escherichia coli means that Escherichia live in the intestines, Pasterella pestis means pasteurella that causes plague, Bordetetia pertussis means bordetella that causes cough, Clostridium tetani means clostridium that causes tetanus, etc.
S.N. Vinogradsky and M. Beijerinck, taking into account the diversity of bacterial metabolism, suggested that the genus name reflect the characters associated with the morphology, ecology, biochemistry and physiology of microorganisms. This is how the names that are the key to the characterization of the microorganism appeared: Acetobacter (acid-forming bacteria), Nitrosomonas (nitrifying bacteria), Azotobacter (bacteria that fix atmospheric nitrogen), Chromobacterium (pigmented bacteria), B. stearothermophiliis (wax heat-loving bacteria), etc.
Sometimes, as an integral part of taxonomy, identification(definition) of microorganisms. However, this is not entirely correct, since identification uses already built classification systems and specific characteristics of microorganisms indicated in the identification keys (tables). Microorganism identification schemes are a kind of test of the quality of the classification system. For the identification of microorganisms, phenotypic and genotypic methods, methods of computer identification analysis and genomic fingerprinting are widely used.
In 1923, D. Bergey released the first international bacterial determinant. Subsequent editions have been prepared by the International Committee on Systematics of Bacteria. The ninth, last American edition of Bergey's Manual of Determinative Bacteriology, was published in 1994. The abbreviated name of the Guide is BMDB-9. In Russian translation, BMDB-9 was published in 1997. It introduces the diversity prokaryotes and takes a step towards attempts to identify microorganisms isolated from the environment.
According to BMDB-9, bacteria are classified (based on phenotypic traits) into four main categories:
1. Gram-negative eubacteria with cell walls.
2. Gram-positive eubacteria with cell walls.
3. Eubageria, devoid of cell walls.
4. Archaebacteria.
The main object in the identification of microorganisms is a pure culture of an isolated bacterium, called a "strain" or "clone".
Strain(from German stammen - to occur) is a bacterial culture of the same species, isolated from different objects or from one object in different time, and characterized by minor changes in properties (for example, sensitivity to antibiotics, enzymatic activity, ability to form toxins). Typically, strains of one species are adapted to a particular habitat.
under the term " bacterial culture» understand the population of microbial cells at a given place and at a given time. These can be microorganisms grown on a solid or liquid nutrient medium in a laboratory. A culture of microorganisms grown on a solid or liquid nutrient medium from individuals of the same species by successive subcultures of a single colony is called clean.
Pure bacterial cultures obtained from a single original cell are called clones(from Greek klon - offspring). A clone is a genetically homogeneous population.
A mixed culture is called a culture of heterogeneous microorganisms isolated from the material under study, for example, from water, soil, air.
Lecture number 2.
SYSTEMATICS AND NOMENCLATURE.
4. Adaptability.
3 domains(or " empire»): « bacteria », « Archaea " And " Eukarya »:
domain " bacteria» eubacteria );
domain " Archaea» archaebacteria ;
domain " Eukarya» Eukarya » includes: kingdom Fungi (mushrooms); animal kingdom Animalia Protozoa ); plant kingdom plantae .
taxonomy [from Greek. taxis - location, order, + nomos taxa
protista [from Greek. protistos eukaryotes [from Greek. eu- - good, kind + karyon prokaryotes [from Greek. pro- preceding + karyon
Systematics of microorganisms.
The natural (phylogenetic) taxonomy of microorganisms has the ultimate goal of uniting related forms, connected by a common origin, and establishing a hierarchical subordination of individual groups.
Until now, there are no common principles and approaches to combining (or separating) them into various taxonomic units, although they try to use the similarity of genomes as a generally accepted criterion for them. Many microorganisms have the same morphological features, but differ in the structure of their genomes, the relationships between them are often unclear, and the evolution of many is simply unknown. Moreover, the cornerstone for each classification concept "view" for bacteria, it still does not have a clear definition, and in some cases the true relationship between bacteria may turn out to be controversial, since it only reflects a common origin from one distant ancestor. Such a simplified criterion as the size, used at the dawn of microbiology, is now absolutely unacceptable. In addition, microorganisms differ significantly in their architecture, biosynthetic systems, and organization of the genetic apparatus. They are divided into groups to demonstrate the degree of similarity and the proposed evolutionary relationship. The basic feature used to classify microorganisms is the type of cellular organization.
Artificial (key) taxonomy of microorganisms, which combines organisms into groups based on the similarity of their most important properties.
These characteristics are used to define and identify microorganisms. From the standpoint of medical microbiology, microorganisms are usually divided according to the effect they have on the human body: pathogenic, opportunistic and non-pathogenic. Despite the obvious importance of this utilitarian approach, their taxonomy is still based on principles common to all forms of life. For
facilitating diagnosis and making decisions regarding the treatment and prognosis of the disease, identification keys are proposed. Grouped in this way, microorganisms are not always in phylogenetic relationship, but are listed together because they have several easily identifiable similar properties. A variety of accessible and rapid tests have been developed that allow, at least in general terms, to identify microorganisms isolated from a patient. With regard to bacteria, the most widespread are the approaches to systematization proposed by the American bacteriologist David Burgi, which take into account one or more of the most characteristic features. "Burgey's Bacteria Key"
– characteristic example artificial systematics. According to his principles, easily detectable properties are
the basis for organizing bacteria into large groups.
Genus and above.
The names of taxa with a genus rank and higher are uninominal (unitary), that is, they are designated by one word, for example herpesviridae (family of herpesviruses).
The names of species are binomial (binary), that is, they are denoted by two words - the name of the genus and the species. For example, Escherichia coli (coli). The second word of the binary name of the species, taken alone, has no status in the nomenclature and cannot be used for the scientific designation of the microorganism. An exception is viruses whose species names are not binary, that is, they include only the species name (for example, rabies virus).
infraspecific taxa.
The taxonomy of bacteria also includes intraspecific taxa, the names of which do not follow the rules of the International Code of Nomenclature for Bacteria.
Subspecies.
The names of the subspecies are trinominal (trinary); the word subspecies is used to designate them ( subspecies ) after the species name, for example Klebsiellapneumoniaesubsp.ozenae (wand ozena, where ozenae - the name of the subspecies).
Option.
Various mechanisms of bacterial variability lead to a certain instability of characters, the totality of which determines one or another species. Therefore, in the taxonomy of bacteria, the concept is widely used. "option" . There are morphological, biological, biochemical, serological and many other options. In medical bacteriology, serological variants (serovars), variants resistant to antibiotics (resistensvars), bacteriophage-resistant (phagovars), as well as variants that differ in biochemical (chemovars), biological or cultural characteristics (biovars) are usually distinguished.
Strain and clone.
In microbiology, specialized terms are also used - " strain " And " clone ».
strain[from him. stamens - occur] is a culture of microorganisms isolated from a certain specific source (any organism or environmental object).
clone[from Greek. clone - layering] is called a culture of microorganisms obtained from one mother cell.
Viroids.
Viroids[from virus and Greek eidos - similarity] - are small circular single-stranded supercoiled RNA molecules (the genome of the hepatitis D virus has a similar organization). Since viroids do not have a protein coat, they do not show pronounced immunogenic properties, and therefore they cannot be identified by serological methods. Viroids cause disease in plants.
Prions.
Included in the realm Vira as an unnamed taxon.
Prions [from English. proteinaceousinfectious (particles ), proteinaceous infectious (particle)] – proteinaceous infectious agents leading to the development of lethal neurological diseases (spongiform encephalopathies). Prion proteins have been isolated as the infectious onset of scrapie in sheep, bovine spongiform encephalopathy ("mad cow disease"), and in humans - kuru, Creutzfeldt-Jakob disease, Gerstmann-Straussler-Scheinker syndrome, and fatal familial insomnia. Prions are transmitted by inoculation or alimentary means not only between individuals of the same biological species, but also between animals. different types including between animals and humans.
The pathogenesis of prion diseases is associated with a change in the nature of the folding of the polypeptide chain, that is, a change in protein conformation. As a result, conglomerates are formed in the form of sticks or ribbons 25~550 × 11 nm in size. These prion protein forms are resistant to boiling, ultraviolet (UV) radiation, 70% ethanol and formaldehyde, and persist in tissues fixed with 10% formalin. Once in a healthy human or animal body, pathological conformers contribute to the gradual deposition of amyloid-like structures, which also include normal proteins. PrP C .
acid-resistant bacteria.
The cell wall of some bacteria contains a large number of lipids and waxes, making them resistant to subsequent discoloration after staining with acids, alkalis or ethanol (for example, types Mycobacterium or Nocardia ). Such bacteria are termed acid-fast and difficult to Gram-stain (although acid-fast bacteria are considered Gram-positive). For their coloring, the Ziehl-Neelsen method is used.
Gram or Ziehl-Neelsen stain is diagnostic for bacteria with a strong cell wall. They are unsuitable for staining mycoplasmas (no cell wall) or spirochetes (cell wall thin and easily destroyed by staining). To study the latter, various methods applying contrasting substrates to their surface (for example, silvering).
Mobility.
An important differentiating feature is mobility. In accordance with the method of movement, gliding bacteria are isolated, moving due to wave-like contractions of the body, and floating bacteria, the movement of which is provided by flagella or cilia.
The ability to spore.
To classify some bacteria, their ability to sporulate, the size of the spores and their location in the cell are taken into account.
Physiological activity.
Physical activity is equally important hallmark. Bacteria are divided according to the method of nutrition, according to the type of energy production (respiration, fermentation, photosynthesis), in relation to pH, indicating the limits of stability and optimum growth, etc. The most important criterion is the ratio to oxygen.
Aerobic bacteria use molecular O 2 as the final electron acceptor during respiration. Most bacteria have membrane-bound cytochrome C-oxidase, which plays a leading role in the electron transport chain. To detect the enzyme, an oxidase test is used, based on the ability of a colorless substance NN -dimethyl- p -phenylenediamine acquire a raspberry color upon reduction.
Anaerobic bacteria do not utilize molecular O 2 as the final electron acceptor. Such bacteria receive energy either in the process of fermentation, where the final electron acceptors are organic compounds, or when anaerobic respiration, using an electron acceptor other than oxygen (for example, NO 3 ¯ , SO 4 2- or Fe 3+).
Optional bacteria can obtain energy either in the process of respiration or fermentation, depending on the presence or absence of oxygen in the environment.
biochemical properties.
To differentiate bacteria, their ability to ferment carbohydrates, form various products (hydrogen sulfide, indole), or hydrolyze proteins is studied.
antigenic properties.
The antigenic properties of various bacteria are specific and associated with structural features of cellular structures recognized by special antisera as antigenic determinants. Typing of bacteria according to antigenic structure is carried out in the agglutination reaction (RA), mixing a drop of antiserum with a drop of bacterial suspension. With a positive reaction, separate aggregated lumps appear in the initially homogeneous bacterial suspension. There are the following types of AG:
genus-specific detected in all representatives of a particular genus, including individual strains;
species-specific detected in individual species and strains of microorganisms;
serovar- (strain-) specific detected in representatives of various subgroups (strains) within a particular species.
Chemical composition.
An important classification feature is the total chemical composition bacterial cells. Usually determine the content and composition of sugars, lipids and amino acids in cell walls.
genetic relationship.
For the phylogenetic classification of bacteria, the best and most informative indicator is genetic relationship. When systematizing bacteria on the basis of genetic relationship, a number of indicators are taken into account.
The ability to exchange genetic information (for example, in the process of transformation or conjugation), possible only between organisms of the same genus or species.
Composition of DNA bases (guanine-cytosine:adenine-thymine ratio).
The similarity of nucleic acids, revealed by the method of hybridization.
Mushroom naming code.
The Fungi Naming Code contains provisions providing for the assignment of separate names to the perfect (sexual, or marsupial) and imperfect (asexual, or conidial) stages. Many fungi have asexual stages ( anamorphs ) and the sexual stages are unknown ( teleomorphs ). Therefore, the code allows you to give different stages (if any) different names. For example, the sexual forms of a yeast fungus Cryptococcus neoformans serovars A And D systematize as Filobasidiellaneoformans var. neoformans or how Cryptococcus neoformans var. neoformans . Teleomorphs serovars IN And WITH- How Filobasidiellaneoformans var. bacillispora or how Cryptococcus neoformans var. gati .
Lecture number 2.
SYSTEMATICS AND NOMENCLATURE.
The paramount, of course, is the question of whether the diversity of forms of existence surrounding us belongs to living or inanimate matter. It is with the development of biology in general and microbiological science in particular, the discovery of known forms life, some established criteria have been put forward that distinguish living matter. These include:
1. Ability to grow and reproduce;
2. Possession of heredity and variability;
3. Exposure to evolution (progressive and regressive);
4. Adaptability.
All existing classifications of life forms are extremely diverse and none of them is complete, comprehensive and universally accepted.
According to the new highest level in the hierarchy of classification among cellular life forms, 3 domains(or " empire»): « bacteria », « Archaea " And " Eukarya »:
domain " bacteria» - prokaryotes, represented by real bacteria ( eubacteria );
domain " Archaea» - prokaryotes presented archaebacteria ;
domain " Eukarya» - eukaryotes, whose cells have a nucleus with a nuclear membrane and a nucleolus, and the cytoplasm consists of highly organized organelles - mitochondria, the Golgi apparatus, etc. Domain " Eukarya » includes: kingdom Fungi (mushrooms); animal kingdom Animalia (includes protozoa - subkingdom Protozoa ); plant kingdom plantae .
Systematics of living organisms is one of the most difficult tasks of biology. Systematics concentrates all the main achievements of science - the more specific they are, the more accurate the classification. Any classification of living organisms is intended to show the degree of similarity and the alleged evolutionary relationship. (with more high categories- capacious and wide, and lower ones - specific and limited). The principles of classification are studied by a special section of taxonomy - taxonomy [from Greek. taxis - location, order, + nomos - law]. Within a particular taxonomic category, there are taxa - groups of organisms, united by certain homogeneous properties.
All existing classifications of life forms are very heterogeneous, none of them is complete, comprehensive and universally accepted. The clear boundaries between the world of plants and the world of animals collapsed after the discovery of microorganisms.
For the third kingdom of living beings, Ernst Haeckel (1866) proposed a collective name protista [from Greek. protistos - first]. All of them are distinguished by a simpler cell structure than in animals and plants. Higher protists (fungi, algae and protozoa) - eukaryotes [from Greek. eu- - good, kind + karyon - nucleus] - have a morphologically distinct nucleus and mitotically divide, which resembles plant and animal cells. A more simply organized group is made up of prokaryotes [from Greek. pro- preceding + karyon – nucleus] – bacteria and blue-green algae, whose cells do not have a membrane around the substance of the nucleus. Later, representatives of the microworld were supplemented by non-cellular life forms - viruses, plasmids, viroids, etc.
Principles of classification of microorganisms.
View – a set of individuals with the same phenotype, producing fertile offspring and living in a certain area.
| For a correct understanding of the meaning of this term in the classification of microorganisms, it is necessary to know the differences in speciation between bacteria and higher plants and animals with obligatory sexual reproduction. The species of the latter are characterized by the presence of populations with a relatively homogeneous set of genes, formed as a result of cross-breeding. If individual parts of a population are isolated from each other (for example, geographically), then their divergent evolution is quite possible. After a certain time, physiological isolation is superimposed on geographical isolation, leading to the development of individual parts of the population along their own path and the formation of a new species. Unlike higher plants and animals, most microorganisms are not able to reproduce sexually. In other words, they lack the mechanisms capable of leading to “discontinuous” speciation. As a result of the filling of various ecological niches, divergent evolutionary forms can develop, but the difference between them is due only to differences between ecological niches. Thus, the definition of species, as applied to sexually reproducing organisms, cannot be fully applied to microorganisms. In this regard, the concept of species for them is interpreted arbitrarily. |
The main stages in the development of microbiology and immunology. Works of L. Pasteur, R. Koch and their importance for the development of microbiology and immunology.
The main stages in the development of microbiology and immunology.
The history of the development of microbiology can be divided into five stages: heuristic, morphological, physiological, immunological and molecular genetic.
Pasteur made a number of outstanding discoveries. In a short period from 1857 to 1885, he proved that fermentation (lactic, alcoholic, acetic) is not a chemical process, but is caused by microorganisms; refuted the theory of spontaneous generation; discovered the phenomenon of anaerobiosis, i.e. the possibility of life of microorganisms in the absence of oxygen; laid the foundations for disinfection, asepsis and antisepsis; discovered a way to protect against infectious diseases through vaccination.
Many of L. Pasteur's discoveries have brought enormous practical benefits to mankind. By heating (pasteurization) diseases of beer and wine, lactic acid products caused by microorganisms were defeated; to prevent purulent complications of wounds, an antiseptic was introduced; Based on the principles of L. Pasteur, many vaccines have been developed to combat infectious diseases.
However, the significance of the works of L. Pasteur goes far beyond just these practical achievements. L. Pasteur brought microbiology and immunology to fundamentally new positions, showed the role of microorganisms in people's lives, economy, industry, infectious pathology, laid down the principles by which microbiology and immunology are developing in our time.
L. Pasteur was, moreover, an outstanding teacher and organizer of science.
L. Pasteur's work on vaccination opened a new stage in the development of microbiology, rightfully called immunological.
The principle of attenuation (weakening) of microorganisms using passages through a susceptible animal or by keeping microorganisms under adverse conditions (temperature, drying) allowed L. Pasteur to obtain vaccines against rabies, anthrax, chicken cholera; this principle is still used in the preparation of vaccines. Consequently, L. Pasteur is the founder of scientific immunology, although before him the method of preventing smallpox by infecting people with cowpox, developed by the English physician E. Jenner, was known. However, this method has not been extended to the prevention of other diseases.
Robert Koch. The physiological period in the development of microbiology is also associated with the name of the German scientist Robert Koch, who developed methods for obtaining pure cultures of bacteria, staining bacteria during microscopy, and microphotography. Also known is the Koch triad formulated by R. Koch, which is still used in establishing the causative agent of the disease.
The role of I. I. Mechnikov in the formation of the doctrine of immunity. Significance of D.I. Ivanovsky's discovery. The role of domestic scientists (I. F. Gamaleya, P. F. Zdrodovsky, A. A. Smorodintsev, M. P. Chumakov, Z. V. Ermolyeva, V. M. Zhdanov, etc.) in the development of microbiology and virology.
After the work of L. Pasteur, many studies appeared in which they tried to explain the causes and mechanisms of the formation of immunity after vaccination. An outstanding role in this was played by the works of II Mechnikov and P. Erlich.
Research by I. I. Mechnikov(1845-1916) showed that special cells - macro- and microphages - play an important role in the formation of immunity. These cells engulf and digest foreign particles, including bacteria. Research by I. I. Mechnikov on phagocytosis convincingly proved that, in addition to humoral, there is cellular immunity. II Mechnikov, the closest assistant and follower of L. Pasteur, is deservedly considered one of the founders of immunology. His work laid the foundation for the study of immunocompetent cells as the morphological basis of the immune system, its unity and biological essence.
D.I. Ivanovsky(1864-1920) discovered viruses - representatives of the vira kingdom. One of the founders of virology. For the first time, he discovered the causative agent of tobacco mosaic passing through bacteriological filters, later called a virus. Works on phytopathology and physiology of plants.
Zdrovsky(1890-1976), Russian microbiologist, immunologist and epidemiologist, academician of the Academy of Medical Sciences. Research on problems of tropical diseases, brucellosis, and others. Under the direction of Zdrodovsky, methods of vaccination against tetanus, diphtheria, and other infections were developed. Author of the book "The Doctrine of Rickettsia and Rickettsia"
Smorodintsev, Russian virologist and immunologist. Proceedings on the etiology and prevention of influenza, encephalitis and other viral infections. Together with M.P. Chumakov developed and introduced the polio vaccine.
Ermolyeva, Russian microbiologist. Received the first domestic samples of antibiotics - penicillin, streptomycin, etc.; interferon.
Zhdanov, Russian virologist. Proceedings on viral infections, molecular biology and classification of viruses, the evolution of infectious diseases.
Basic principles of classification of microbes.
Microbes, or microorganisms(bacteria, fungi, protozoa, viruses) are systematized according to their similarities, differences and relationships with each other. This is done by a special science - the systematics of microorganisms. Systematics includes three parts: classification, taxonomy and identification. The taxonomy of microorganisms is based on their morphological, physiological, biochemical and molecular biological properties. The following taxonomic categories are distinguished: kingdom, subkingdom, department, class, order, family, genus, species, subspecies, etc. Within the framework of a particular taxonomic category, taxa are distinguished - groups of organisms united according to certain homogeneous properties.
Microorganisms are represented by precellular forms (viruses - the Vira kingdom) and cellular forms (bacteria, archaebacteria, fungi and protozoa). There are 3 domains(or "empires"): "Bacteria", "Archaea" and "Eukarya":
□ "Bacteria" domain - prokaryotes represented by true bacteria (eubacteria);
□ "Archaea" domain - prokaryotes represented by archaebacteria;
□ "Eukarya" domain - eukaryotes whose cells have a nucleus with a nuclear membrane and a nucleolus, and the cytoplasm consists of highly organized organelles - mitochondria, the Golgi apparatus, etc. The "Eukarya" domain includes: the Kingdom of Fungi (mushrooms); the animal kingdom Animalia (includes the simplest - the sub-kingdom Protozoa); plant kingdom Plante. Domains include kingdoms, types, classes, orders, families, genera, species.
View. One of the main taxonomic categories is the species (species). A species is a collection of individuals united by similar properties, but different from other members of the genus.
pure culture. 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 a pure culture.
Strain. A pure culture of microorganisms isolated from a specific source and different from other representatives of the species is called a strain. A strain is a narrower concept than a species or subspecies.
Clone. Close to the concept of a strain is the concept of a 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 is used var(variety) instead of the previously used type.
Similar information.
Viruses- the smallest microbes that do not have a cellular structure, a protein-synthesizing system, containing only DNA or RNA. They belong to the kingdom of Vira. Being obligate intracellular parasites, viruses multiply in the cytoplasm or nucleus of the cell. They are autonomous genetic structures. They differ in a special - disjunctive (disjunctive) method of reproduction (reproduction): nucleic acids of viruses and their proteins are synthesized separately in the cell, then they are assembled into viral particles. The resulting viral particle is called a virion.
Form virions can be different: rod-shaped (tobacco mosaic virus), bullet-shaped (rabies virus), spherical (polio viruses, HIV), in the form of sperm (many bacteriophages). Distinguish between simple and complex viruses. Simple, or non-enveloped, viruses They are made up of a nucleic acid and a protein coat called a capsid. The capsid consists of repeating morphological subunits - capsomeres. The nucleic acid and the capsid interact with each other to form the nucleocapsid. Complex or enveloped viruses outside the capsid are surrounded by a lipoprotein membrane (supercapsid, or peplos). This shell is a derivative structure from the membranes of a virus-infected cell. On the envelope of the virus are glycoprotein spikes, or spines (peplomers). Under the shell of some viruses is the matrix M-protein.
Symmetry type. The capsid or nucleocapsid may have helical, icosahedral (cubic) or complex symmetry. icosahedral the type of symmetry is due to the formation of an isometric hollow body from a capsid containing a viral nucleic acid (for example, in hepatitis A, herpes, poliomyelitis viruses). Spiral the type of symmetry is due to the helical structure of the nucleocapsid (for example, in the influenza virus).
Inclusions- accumulation of virions or their individual components in the cytoplasm or nucleus of cells, detected under a microscope with special staining. The variola virus forms cytoplasmic inclusions - Guarnieri bodies; herpes viruses and adenoviruses - intranuclear inclusions.
Viruses have a unique genome because they contain either DNA or RNA. Therefore, a distinction is made between DNA-containing and RNA-containing viruses. They are usually haploid, i.e. have one set of genes. The genome of viruses is represented various types nucleic acids: double-stranded, single-stranded, linear, circular, fragmented. Among RNA-containing viruses, viruses with a positive (plus-strand RNA) genome are distinguished. The plus-strand RNA of these viruses performs the hereditary function and the function of messenger RNA (mRNA). There are also RNA-containing viruses with a negative (negative-strand RNA) genome. The negative strand of RNA of these viruses performs only a hereditary function. In addition to common viruses, the so-called non-canonical viruses - prions - protein infectious particles, which are agents of a protein nature, are also known, having the form of fibrils with a size of 10-20x100-200 nm. Prions, apparently, are both inducers and products of an autonomous human or animal gene and cause encephalopathy in them under conditions of a slow viral infection (Creutz-feldt-Jakob disease, kuru, etc.). Other unusual agents close to viruses are viroids - small circular, supercoiled RNA molecules that do not contain protein that cause diseases in plants.
Antigens: definition, basic properties.
Underantigenicity understand the potential ability of an antigen molecule to activate components of the immune system and specifically interact with immune factors. In other words, the antigen should act as a specific stimulus in relation to immunocompetent cells. At the same time, the interaction of the immune system component does not occur with the entire molecule at the same time, but only with its small area, which is called the "antigenic determinant" or "epitope". Immunogenicity- the potential ability of an antigen to cause a specific protective reaction in relation to itself in the macroorganism. The degree of immunogenicity depends on a number of factors that can be combined into three groups: 1. Molecular features of the antigen; 2. Clearance of the antigen in the body; 3. Reactivity of the macroorganism. To the first group of factors the nature, chemical composition, molecular weight, structure and some other characteristics are assigned. Great importance has the size and molecular mass antigen.
The second group of factors associated with the dynamics of antigen entry into the body and its excretion. The amount of incoming antigen affects the immune response: the more it is, the more pronounced the immune response. The third group combines factors, which determine the dependence of immunogenicity on the state of the macroorganism. In this regard, hereditary factors come to the fore.
Specificity called the ability of an antigen to induce an immune response to a strictly defined epitope. This property is due to the peculiarities of the formation of the immune response - the complementarity of the receptor apparatus of immunocompetent cells to a specific antigenic determinant is necessary. Therefore, the specificity of an antigen is largely determined by the properties of its constituent epitopes.
Bacterial cell antigens. In the structure of a bacterial cell, flagella, somatic, capsular and some other antigens are distinguished. Flagella,orH-antigens, localized in the locomotor apparatus of bacteria - their flagella. They are epitopes of the contractile protein flagellin. When heated, flagellin denatures and the H-antigen loses its specificity. Phenol does not act on this antigen. Somatic,orO antigen associated with the bacterial cell wall. Its basis is LPS. O-antigen exhibits thermostable properties - it is not destroyed
At the stage of its formation, that is, in the XVII-XVIII centuries, microbiology developed in such a way that all the organisms found were described without introducing any logical classification. At that time, microbiology described microorganisms in a morphological way. Significant changes took place in the 19th century. By this time, scientists have accumulated a fairly voluminous knowledge base, and have also found a wide variety of microorganisms, fungi. To somehow navigate in this abundance of information, a logical structure was required. This was proposed in 1923, when a determinant of bacteria was published. This was the first international work that became the basis for the development of the science of microbiology.
Basic provisions
A single classification was officially introduced at the international level in 1980. It is based on the system developed by Bergi. Key steps: kingdom, class, order, family, genus, species. The latter is the most significant level for the system of division into classes. It unites organisms that have a number of similarities: morphology, origin, physiology. In addition, the features of metabolism are analyzed. If it turns out to be highly similar, then the microorganisms can be grouped into a species.
Types of microorganisms can be divided into two categories:
- eukaryotes;
- prokaryotes.
The second group includes bacteria, that is, organisms lacking a formalized nucleus. DNA includes all the data necessary for the normal inheritance of traits. The DNA molecule is located in the cell cytoplasm.
One level down
View is not the best low level classification of microorganisms. Inside it there are:
- morphovars, which are characterized by a special morphology of microorganisms;
- biovars that differ in biology;
- chemovars, which are characterized by a slightly different activity of enzymes;
- serovars allocated into groups depending on the antigenic structure;
- fagovars, the classification of which is based on the susceptibility of phages.
Everything is accounted for and recorded
In order to standardize the classification of microorganisms into biological groups, a system of notation was introduced at the international level for different groups. It is based on the idea of binarity, that is, a double nomenclature is used. The name begins with the name of the genus - this word is always written with a capital letter. But the second word starts with a small one, it describes belonging to a species. For example: Staphylococcus aureus.
Medical microbiologists: what will we pay special attention to?
Traditionally pathogenic microorganisms are a topic that attracts physicians involved in microbiology. The focus is on various representatives - viruses, bacteria, chlamydia and others. Microbes are indistinguishable for the human eye, and in order to see them, you need to use a special technique - microscopes that magnify the object under study many times over.
Pathogenic microorganisms of interest to medicine and science include non-cellular viruses and those microscopic life forms that are composed of a large number of cells. These are various fungi, chlamydobacteria, algae that are dangerous to humans (and not only).
Basic terms: bacteria
What are microorganisms? For different categories, there are different explanations that allow you to figure out what the group of life forms of interest is. For example, it is customary to call bacteria such organisms, which include only one cell. A feature of bacteria is the absence of chlorophyll. Classification of microorganisms of this group - prokaryotes. Some bacteria are as little as 0.1 micrometers, but some reach 28 micrometers. The forms of these organisms depend on the habitat. She defines the dimensions.
All bacteria known to science are usually divided into groups:
- cocci (balls);
- sticks (bacilli, clostridia);
- threads (chlamydobacteria);
- curly (spirilla, etc.).
Classifications of microorganisms: more
Kokkam is characterized by the shape of a sphere, ellipse, bean, ball. Also found in the form of a lancet. Types of microorganisms of this group: diplo-, micro-, strepto-, tetra-, staphylococci, sarcins.
Micrococci are characterized by randomness of cells, but this condition is not necessary: they meet those that include only one or two cells. All these microorganisms are considered saprophytes. Their habitat is air, water.
Diplococci divide to form paired cocci. A typical representative is the provoking meningitis meningococcus, as well as the source of gonorrhea gonococcus. Like diplococci, twisted streptococci can divide in the same plane, but their peculiarity is the presence of different-sized chains. These microbes and bacteria are dangerous, excite various diseases, even leading to death.
What else is there?
What are tetracocci microorganisms? The name itself speaks of the distinctive feature of such life forms: tetra in Latin means “four”. Such microorganisms are able to divide in planes, perpendicular each relative to a friend. For humans, they are relatively safe: so far, few diseases provoked by tetracocci are known.
Sardine cocci are known. They are characterized by division in three planes perpendicular to each other. Visually, organisms look like bales. They usually contain 8-16 cells. Among the habitats of these microorganisms is the air. The human diseases provoked by them are not known to science, therefore, at the moment it is believed that they do not exist.
But the significance of staphylococcal microorganisms was discovered by scientists quite a long time ago - they provoke skin diseases that affect not only humans, but also various animals. Visually, organisms are like clusters. Division is available in different planes. Usually live in clusters, the form is chaotic.
sticks
According to the classification of microorganisms, this group includes bacteria, bacilli, clostridia. The usual size is 1-6 microns long, 0.5-2 microns wide. Rod bacteria do not form spores. Dangerous forms are known: intestinal, tuberculosis, diphtheria and others. Bacilli, clostridia - microbes that create spores. They provoke a variety of dangerous (even fatal) infections: anthrax, hay fever, tetanus.
Allocate short sticks, long, and also with different ends: round, sharp. Description of the morphology of microorganisms involves the study of the relative position. This parameter became the basis for the division into three groups:
- paired arrangement;
- unsystematic;
- streptobacilli, streptobacteria.
The first provoke pneumonia, the second group causes a very wide range of diseases, and the third - anthrax, soft chancre.
Less commonly, bacteria can be observed, at the ends of which there is a thickening resembling a club shape. The current classification of microorganisms involves classifying them as rods. Distinctive feature of this group - a stick can provoke diphtheria, and a number of subspecies - leprosy, tuberculosis.
Twisted microorganisms
Vibrios belonging to this group are bent into 14 turns and are similar in shape to the symbol ",". These include widespread vibrios: cholera, water. Spirilla, related to twisted microorganisms, are distinguished by a bend in one or more turns. Science knows only one dangerous to man view - it provokes sodoku. This disease can be obtained if bitten by a rodent (for example, a rat).
Spirochetes are corkscrew-like microorganisms 0.3-1.5 µm long, 7-500 µm wide. This includes saprophytes, some other dangerous species. The nutrient media of microorganisms are dirty waters, dead masses. There are three known species that provoke diseases in humans: Borrelia, Leptospira, Treponema.
General features of twisted microorganisms
All the groups described above are polymorphic. This means that the external environment determines the shape, size. Significant are:
- temperature;
- the influence of drugs;
- presence of disinfection.
Laboratory diagnosis obliges to take into account the ability of bacteria to change. Also, these features affect the development, production of drugs used in the prevention and treatment of diseases.
Don't run away
Academician Omelyansky once wrote that microbes are invisible, but they are always next to a person, like friends and enemies. These microscopic forms of life fill the air, soil, water, are in the human body, in any animal. Some can be used for human benefit, which is especially true for Food Industry, but many are deadly, as they provoke diseases. It is because of microbes that food can spoil.
Microbes were first discovered in XVII century when it was possible to design lenses with 200x magnification. The microcosm amazed the scientist who first saw it, the Dutchman Leeuwenhoek. Some time later, the research was continued by Pasteur, who revealed the specifics of the vital activity of microscopic life. For example, it was possible to explain the fermentation of alcohol, some human diseases. Then the first vaccine was invented. The first diseases defeated by this method were anthrax and rabies.
Special Features: microbes
This group includes organisms (mostly consisting of one cell), which can be seen only at high magnification. The sizes of most microbes known to science range from a thousandth of a millimeter to a thousandth of a micrometer. There are a huge number of species of this life form. Different microbes can exist in different environments. There are categories:
- bacteria;
- phages;
- mushrooms;
- yeast;
- viruses.
There is also a classification:
- mycoplasmas;
- rickettsia;
- protozoa.
Microscopic Life: Spore Formation
The process is not easy, the spores are not at all the same as a bacterial cell. Spores are protected by a dense shell, inside which is a small volume of liquid. The spore does not need a nutrient; reproduction processes freeze. This form of life exists for a long time in the most unpleasant conditions: sub-zero temperatures, in heat or drying. Some disputes are viable for decades, centuries. Microorganisms that provoke tetanus, anthrax and botulism are considered such dangerous. As soon as the environment becomes comfortable for existence, the spore grows and begins to multiply.
Bacteria: structure
A normal bacterial cell consists of a membrane and a mucous membrane, often forming a capsule. Inside - the cytoplasm, protected by a membrane. Cytoplasm is a colorless protein in colloidal form. Inside the cytoplasm - ribosomes, nucleus, DNA. Here the cell stores nutrients.
There are bacteria that can move. To do this, nature endowed them with thin threads called flagella. The cords rotate, which pushes the bacterium to a new habitat. Some have bundles, others have single strands. There are bacteria in which tourniquets are located over the entire surface. Most often, tourniquets are observed in sticks, twisted forms. But the cocci of flagella in the bulk are deprived, therefore this type of microscopic life is motionless.
Reproduction - division. Some divide every 15 minutes, so the growth of the colony is rapid. This is most often observed in foods enriched with nutrients.
This is a rather specific, unlike anything else group of microscopic life. Viruses known to science range in size from 8 to 150 nm. They are examined only through the system of modern magnification - an electron microscope. Some contain protein and acid. Microscopic organisms provoke many diseases, among them - measles, hepatitis. Infect animals, initiating plague, other disorders, including the very dangerous foot and mouth disease.
Bacterial viruses known to science are designated by the term "bacteriophages", but "mycophages" work against fungi. The former can be found wherever microscopic life occurs. They provoke the death of the microbe, therefore they are used for therapeutic, prophylactic purposes, and are effective for infections.
Rickettsia and mushrooms
Mushrooms are also a very interesting group of microorganisms. Their feature is the absence of chlorophyll. Such a life form is not capable of producing organic matter, but needs it in order to exist. This determines the substrates on which fungi can survive: the environment must be rich in nutrients. Mushrooms infect humans, provoke diseases of insects, animals, even plants. It is they who call for the most unpleasant diseases of the potato familiar to us - cancer, late blight.
Fungal cells consist of a vacuole, a nucleus. Visually similar to plant cells. Form: long branches. The cell consists of threads woven together, called hyphae by scientists. GIFs - construction material for mycelium, consisting of cells (with 1-2 nuclei). However, mycelia are known, which are one cell with big amount nuclei. These are called non-cellular. The mushroom picker is the base for the growth of the fruiting body. However, such fungi are known that consist of one cell and do not need mycelium.
Mushrooms: features
Science knows different ways of reproduction of mushrooms. One of them is the division of hyphae, that is, the vegetative method. Most fungi reproduce by spores, and the division is sexual, asexual. Spores can survive in the most hostile environments for centuries. Ripe spores "travel" long distances using carriers before germination. As soon as the spore is in a medium rich in nutrients, it germinates, filaments, mycelium appear.
Many fungi known to science belong to the mold category. Under natural conditions, they are found in a variety of places. Microorganisms are especially willing to germinate on food. It is easy to see them - a colored coating appears. Most often in everyday life, a person encounters mucosal fungi that form a white, rather fluffy mass. If the vegetables are covered with "soft" rot, rhizopus probably appeared here. But if there is a thin film on pears, apples, then the reason is probably in botrytis. Quite often, mold is provoked by penicillium microorganisms.
Danger and benefit
Mushrooms not only spoil food, but poison. Microorganisms producing mycotoxins are capable of this: Fusarium, Aspergillus.
However, mushrooms useful to humans are known. They are quite widely used in the manufacture of medicines, food. Thus, penicillium is indispensable in the manufacture of penicillin, an antibiotic used in a wide range of diseases. You can not do without it in the manufacture of noble, expensive cheeses - Roquefort, Camembert. Aspergillus is necessary for enzyme preparations, it is used in the manufacture of citric acid.
mushroom bacteria
Another interesting group of microscopic organisms discovered by scientists is actinomycetes. They have some properties of fungi, but at the same time they have signs of bacteria. They are connected with the first by the method of reproduction, the presence of mycelium, hyphae. Common features with bacteria - a feature of the structure, biochemistry.
Yeast
Finally, yeast are such microscopic organisms that consist of a single cell. Yeast cannot move, grow up to 10-15 microns. Mostly they are oval, round, but they are also found in the form of sticks, sickles. Occasionally even come across similar in shape to lemons. Cell structure similar to characteristic of mushrooms, there is a vacuole, a nucleus. Yeasts divide, form spores, and reproduce by budding.
IN natural conditions there is a wide variety of yeasts. They live on plants, eat in soil, food, waste - wherever there is sugar. In food, yeast causes spoilage, as the products turn sour and begin to ferment. There are also forms that produce carbon dioxide, alcohol from sugar. They have been actively used by man for a long time for the manufacture of alcoholic beverages. There are also types of yeast that are dangerous to human health - these provoke candidiasis. To this day, the fight against parasitic fungi is very difficult, and candidiasis in some forms can even lead to death (for example, systemic).
