MEDIUMS

From Big Medical Encyclopedia

MEDIUMS - the artificial substrates representing the balanced mix of nutrients in the concentration and combinations creating the best conditions for growth of microorganisms.

Items of page use for cultivation of microorganisms in a laboratory and work practice, for studying of properties of the microorganisms allocated from an organism (at diagnosis inf. diseases) or from the environment, for storage and preservation of pure growths of microorganisms. The nutrients which are P.'s part of page are necessary for biosynthesis structural and biochemical, components of microorganisms and for obtaining energy by them. All chemical reactions in live organisms proceed in an aqueous medium therefore water — an important component any P. of page and carries out in it a role of a source of oxygen and hydrogen.

The best source of carbon for microorganisms — carbohydrates. Monosaccharides, especially hexoses, are widely used by many microorganisms. One of the carbohydrates which are most widely consumed by microorganisms is glucose. A good source of carbon for many fungi and an actinomyce — a mannitol. Actinomycetes are capable to use glycerin as a source of carbon. Organic to - you are also a source of carbon, however they can lead to decrease in pH of the environment and slow down growth of microorganisms therefore apply salts organic to more often - t. Nek-ry organic to - you (lemon, wine) cause in P. page a lack of ions of metals that also influences growth of microorganisms. Amino acids are a good source of carbon and provide the needs of microorganisms for it. As a source of carbon different microorganisms can use various connections. So, e.g., nek-ry bacteria of the sort Pseudomonas are capable to use any of 90 various organic compounds as a source of carbon and energy, including sugar, fat to - you, organic to - you and amino acids, and the bacteria oxidizing methane utilize as a source of carbon and energy only methane and methanol.

In P. the source of nitrogen, available to microorganisms, which is necessary for synthesis of the amino acids necessary at creation of cellular proteins, for synthesis of the purine and pirimidinovy bases — structural elements nucleinic to - t shall be page. As a source of nitrogen fungi and nek-ry bacteria use nitrates, to-rye at first are recovered by microorganisms and only after that are used in processes of biosynthesis. Very many microorganisms need the recovered nitrogen therefore for their cultivation pages as a source of nitrogen bring salts of ammonium in P. The need of microorganisms for nitrogen can be satisfied at the expense of organic compounds, napr, amino acids, or more difficult products of incomplete disintegration of proteins-peptones. These connections can be a source not only of nitrogen, but also carbon, sulfur, and also energy. Therefore P. the pages containing in quality of substrate of a squirrel of an animal or plant origin or products their chemical or zymolysis, provide growth and development of the vast majority of microorganisms.

Phosphorus is necessary for microorganisms for synthesis of a number of the major components of a cell (DNA, RNA, ATP and so forth). Phosphates can be a source of phosphorus in P. of page. A source of phosphates in natural mediums (broths) are nucleinic to - you or products of their splitting (oligonucleotides, nucleotides).

As a source of sulfur in P. of page bring sulfates, and in the mediums prepared from proteins of a natural origin or products of their disintegration, nek-ry amino acids (cystine, cysteine) are a source of sulfur.

In P. of page there have to be mineral connections. The need of microorganisms for mineral elements is various. Villages add mineral substances to P. — potassium, magnesium, calcium, and also microelements — iron, cobalt, copper, molybdenum, zinc, manganese. Function of mineral connections in metabolism of microorganisms comes down generally to activation of enzymes.

A number of bacteria — representatives of the sorts Haemophilus, Corynebacterium, Lactobacillus, Brucella and some other — requires existence in P. of page of growth factors (see. Bacterial growth factors ), i.e. the connections necessary for life activity of microorganisms, but not synthesized by them. Amino acids, vitamins, the purine and pirimidinovy bases, etc. are among such substances.

One of the important factors defining P.'s quality of page is the optimum concentration of hydrogen ions estimated by an indicator of pH and preservation of reaction of the environment in the optimum range for this microorganism at its cultivation. Limiting values of pH of the environment for microorganisms 4,0 — 9,0, most often the optimum of pH is close to neutral. Pathogenic microorganisms grow on Wednesdays which pH 7,2 — 7,4 better, and fungi — at pH 4,0 — 6,0. Bacteria do not grow on Wednesdays which pH lower than 4,0. An exception are the acetic-acid bacteriums and sulfuric bacteria oxidizing sulfur to sulfuric to - you.

Metabolic activity of the cultivated microorganisms can lead to shift of reaction of the environment both in acid, and in the alkaline party. Not to allow it, villages add buffers to P. Most often at P.'s preparation by the village use the phosphatic buffers consisting of mix of monosubstituted and disubstituted phosphates (K2HP04 and KH2P04). The maximum concentration of phosphate in the environment transferred by bacteria and fungi corresponds to 0,5%.

The item of page depending on their properties and appointment can be divided into groups. On a consistence they are divided on dense, liquid and semi-fluid. A number of the substances condensing P. with page was offered (methyl cellulose, starched gel, etc.). Practical use found an agar — the polysaccharide emitted from algas (see. Agar ), gelatin (see) and the silica gel representing silicon dioxide. An agar pages in concentration usually bring 1 — 2% in P., to gelatin — 10 — 15%, and silica gel — 1,5%. Wednesdays from gelatinous use only in the special purposes since gelatinous gel melts at t ° 25 — 30 °, i.e. below an optimum of growth of the majority of pathogenic bacteriums. In semi-fluid environments concentration of an agar is reduced to 0,2-0,4%.

On character of the ingredients which are P.'s part of page they are divided into P. by the pages of unknown chemical structure based on proteins and products of their hydrolysis, and the circle of the famous structure (synthetic environments). Items of page of unknown chemical structure can be simple (main) and difficult. The main ingredients of simple P. of page — the decomposition products of proteins received by enzymic or acid hydrolysis. Enzymic hydrolysis is carried out by means of partially purified proteolytic enzymes (pepsin, trypsin, papain) or by processing of a feed stock (meat, fish, a placenta) the fabrics containing these enzymes, napr, a pancreas, crushed by pork stomachs (see. Marten broth , Hottingera agar ). Processing by enzymes of animal protein is not followed by their full hydrolysis therefore are formed so-called. peptones (see). On P. of the pages containing peptones microorganisms breed better, than on full hydrolyzates of protein or on mixes of amino acids since at enzymic hydrolysis of animal or vegetable fabrics in them labile growth factors remain. About degree of hydrolysis of proteins in an initial semi-finished product judge by contents in it the general and amine nitrogen. E.g., on Hottingera the amount of the general nitrogen is equal in a meat repitch to 1100 — 1200 mg / 100 to ml, amount of amine nitrogen 650 — 700mg/100 to ml that corresponds to the albuminolysis equal to 55 — 60%. It is necessary for growth of microorganisms that in 100 ml of broth 250 — 300 mg of the general nitrogen of which 25 — 30% are made by amine nitrogen contained.

On the basis of simple P. pages prepare difficult, napr, the Wednesdays containing various sugar (sugar broth, a sugar agar) or blood (see. Borde — Zhangu a medium , Levintalya of the environment , Fayldsa Wednesday , Tseysslera Wednesday ). Carry the Wednesdays containing blood serum, and Wednesdays with addition of ascitic liquid to difficult P.' number of page of a natural origin. E.g., for cultivation of cocci use the serumal agar containing 10 or 20% of blood serum of a horse or a bull or serumal broth — a beef-extract broth (see. Broth beef-extract ) double concentration, 8 — 10% of blood serum are added to Krom. Nek-ry bacteria (meningokokk, gonokokk) grow in the presence of human protein better. Therefore for their cultivation pages bring ascitic liquid in P. Ascites broth and ascites agar prepare pages to which they add up to 30% of ascitic liquid on the basis of simple P. It is possible to carry milk environments, egg environments to difficult P.' number of the page prepared on the basis of simple environments.

All above-mentioned environments belong to so-called natural circles of unknown structure since they contain nutritious substrates of a natural origin. At the same time control of growth and cultivation of bacteria is more effective if to use P. of page of the famous structure, watered and chemically pure connections in certain concentration. Such environments are called synthetic mediums (see). They have advantage before other P. of page during the studying of features of metabolism of microorganisms since give the chance to investigate and estimate metabolic reactions depending on contents in the environment of these or those components. Complexity of structure of synthetic P. of page depends on biosynthetic activity of microorganisms, i.e. on their need for ready growth factors. If many growth factors are necessary for growth of bacteria, then synthetic P. of page are very difficult on the structure. E.g., cultivation of bacteria of Leuconostoc mesenteroi-des requires existence in synthetic P. of page acetic to - you, 19 amino acids, 4 purines and pyrimidines and 10 vitamins. Difficult P. pages prepare on the basis of the minimum P. pages which part water, mineral salts, a source of nitrogen, most often NH is 4 Cl, and source of carbon and energy, usually glucose or other easily acquired carbohydrate. Villages add necessary growth factors to this minimum P. E.g., L-amino acids in number of 10 — 20 mkg/ml. It is necessary to consider that D-isomers of amino acids can oppress growth of bacteria. Purines, pyrimidines, nucleosides and nucleotides usually bring in synthetic P. page in final concentration to 10 mkg/ml, vitamins — TO 1 mkg/ml.

According to the destination P. pages divide into the selection (elective) and differentsialno - diagnostic. At the selection P.' use by the village it is possible to select the allocated microorganism from the mixed cultures or the studied material by creation of the conditions favorable for its cultivation and adverse for the accompanying microorganisms of other types. The selection P. of page are, e.g., alkaline peptone water and an alkaline agar on which cholera vibrioes are well cultivated. The selection conditions sometimes arise in P. of page as a result of metabolic activity of the allocated microorganism. So, accumulation of lactobacilli is carried out in the environment containing an organic source of growth factors and nitrogen, napr, a yeastrel and glucose. After seeding on such environment of polymicrobial material (raw milk, pieces of vegetables, drain waters) and incubations under anaerobic conditions in P. the page gradually collects milk to - that. Wednesday is intensively acidified that does not interfere with development of lactobacilli, but oppresses (inhibits) growth of other bacteria, in particular bacteria this. Enterobacteriaceae. As P. of page, the selection for pathogenic representatives this. Enterobacteriaceae, use the Wednesdays containing bile, bilious broth (10 — 20% of bile), Kauffmann's circle (see. Kauffmapna Wednesday ). The selection conditions for bacteria this. Enterobacteriaceae create also by addition in P. page of some dyes: malachite green, tetraethyl-diamino-triphenyl-carbohydride sulfate, crystal violet, methylene blue and other, growth-inhibiting gram-positive bacteria. In some cases as a factor of direct selection of the bacteria steady against antibiotics or other antibacterial means, in P. villages add this substance to concentration at which cells of so-called wild type perish, and steady individuals remain. Antibiotics use in the selection P. page not only for direct selection, but also for mediated. As an example it is possible to point pages to which penicillin or ampicillin is added to liquid synthetic P. On these Wednesdays it is possible to select any auxotroph mutants (see. Auksotrofny microorganisms ). The principles of «work» of these Wednesdays are based on ability of antibiotics to suppress growth of the breeding bacteria. The auxotroph mutant does not grow in the minimum environment therefore he does not perish under the influence of the specified antibiotics and it is easy to allocate it then on full-fledged environments.

Are eurysynusic so-called. differential and diagnostic environments (see), the specific features of their metabolism allowing to reveal at microorganisms and by that to otdifferentsirovat the allocated microorganism from others related, but differing in the metabolism (see. Levina Wednesday , Russell Wednesday , Endo Wednesday ). For P.'s standardization by the village that is necessary for obtaining the repeating comparable results, widely use dry P. of page, to-rye represent the pages of various structure which are dried up to a powdery state by P. Wide popularity P. got the pages released by the American firm of Difko. They are used both for cultivation of various microorganisms, and for differential microbiological diagnosis. The USSR makes dry P. of page for cultivation of various microorganisms (dry nutrient broth, dry nutrient agar), and also the environment of a special purpose, napr, for cultivation and allocation of causative agents of a brucellosis and a tularemia, pathogenic clostridiums, diphtheritic bacteria, bacteria this. Enterobacteriaceae, mycobacteria, etc.



Bibliography: Kozlov Yu. A. Mediums in medical microbiology, M., 1950; Rose E. Chemical microbiology, the lane with English, page 65, M., 1971; The Guide to microbiological diagnosis of infectious diseases, under the editorship of K. I. Matveev, page 270, etc., M., 1973; The Reference book on microbiological and virologic methods of a research, under the editorship of M. O. Birger, page 41, M., 1973; Steyniyer R., Edelberg E. and Ingram Dzh. The world of microbes, the lane with English, t. 1, page 46, M., 1979.


L. A. Zamchuk.

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