BACTERIAL CULTURE

From Big Medical Encyclopedia

BACTERIAL CULTURE — set of the bacteria which grew on a solid or liquid medium.

For B.'s receiving to. there is enough entering into a medium at least of one microbic cell, at optimal conditions the large number of generations for a short time gives edges. Speed of reproduction depends on features of this bacterial look and on conditions of growth (a medium, pH, temperature, aeration, etc.). B.'s growth to. in a liquid medium it is shown in opacification of Wednesday, sludge formation or a top skin. On a dense medium of a bacterium form colonies (see. Colony bacterial ), to-rye have characteristic morphology and along with type of growth serve as the test for identification in a liquid medium. During the seeding of a large number of bacteria on the surface of dense nutrient medium the continuous growth of culture of bacteria — a lawn is formed. If on a medium bacteria of one look grow, the culture is considered pure. Mix of two or more species of bacteria carries the name of the mixed B. to. Under natural conditions bacteria are in associations and at crops grow by mediums in the form of the mixed cultures. Pure B.' allocation to. demands use of the special methods based or on mechanical dissociation of bacterial cells, to-rye then are grown up separately, or on use biol, features of bacteria of the allocated look, to-rye allow to exempt them from the accompanying bacteria. In pure growth check specific accessory of bacteria by means of the system of tests including studying of morphology and a complex of biological properties (see. Identification of microbes ). Pure B.'s allocation to. and its identification make a basis of a bacteriological research (see. Bacteriological techniques ). After allocation and identification pure B. to. call strain (see).

B. to. with various degree of deviations from the properties characteristic of this look, carry the name of atypical. Deviations can concern only one property often important in system of the tests used for identification or a number of properties. In the latter case identification by standard methods is difficult. The principles of identification of atypical B. to. are based on attempts of their reversion, and also on use of additional biochemical and biophysical methods of a research.

B. to., grown up on various mediums, carry the corresponding names — agar culture, gelatinous, bouillon. For agar B.'s receiving to. apply mediums where it is added agar (see) in the concentration depending on research objectives and a species of microorganism. On the surface of solid nutrient medium apply concentration to cultivation of bacteria an agar agar of 1 — 2%.

At concentration of 0,7% and the agar is lower call soft or semi-fluid and use for seeding of bacteria in depth of Wednesday. Seeding of bacteria in a medium from gelatinous is applied only with the special purposes since the gel (10 — 15%) formed gelatinous melts at t ° 25 ° and liquefied by proteolytic enzymes of bacteria. For many researches as a starting material serves bouillon B. to., grown up during the night in the thermostat (about 16 — 18 hours). After cultivation in the fresh environment and a podrashchivaniye it is easy to receive bacterial population in any growth phase. At high concentration of cells in fast-growing B. to. aerobes it is necessary to resort to aeration for replenishment of the oxygen content in the environment (the aerated B. to.). Apply or stirring of a small amount of the environment in a vessel of rather large volume, or a transmission through the environment of sterile air. Aeration is widely applied in a work practice at cultivation of bacteria in reactors of large volumes (deep B. to.).

Pure B. to., growing on a medium, represents population of genetically identical individuals. Nevertheless these individuals can differ from each other on a row fiziol, signs: by the sizes, structure of a cellular cover, I will increase and so forth. A part of distinctions manages to be eliminated at synchronization of division of bacteria. The principle of receiving synchronous B. to. consists in a stop of division of bacteria influence physical. or chemical factors at preservation fiziol, activities. After elimination of the factor detaining division, bacteria begin to share at the same time. Synchronism of division comes to light most accurately during the first 2 — 3 generation.

Quantitative assessment of reproduction of bacteria in culture is carried out determination of any size characterizing intensity of reproduction. Depending on research objectives as such size the lump of bacteria or number of separate microorganisms can serve in 1 ml of culture. With B.'s growth to. the weight and number of bacteria change independently from each other, and in different growth periods the relation of lump to number of bacteria fluctuates. The nature of process of reproduction of B. to. finally is defined by system, in a cut there is a reproduction. In the closed system at the limited volume of the environment (a test tube with broth) distinguish several consecutive phases of reproduction, to-rye come to an end with death of a part of population (see Bacteria). In line culture, napr, in an open circuit of type hemostata (see), reproduction of bacteria is continuously supported by giving of the fresh environment and simultaneous removal of a part of biomass of bacteria. Concentration of bacteria is regulated by the speed of receipt of the fresh environment and depends on concentration of one or several limiting metabolites.

B.'s preservation to. shall provide constancy of structure of bacterial population during beyond all bounds long time. It is reached by maintenance of viability of the maximum number of the bacteria taken for preservation since at death of a considerable part of population there is always a possibility of selection of options. The stock culture is rassevat on cups for receiving the isolated colonies. Having convinced of lack of pollution, select several tens of colonies for receiving subcultures. It excludes, on the one hand, a possibility of selection of mutants because of their rarity, on the other hand, prevents selection of often found options of not mutational nature, possible at elimination of single colonies. At preservation by method of freeze drying of subculture of colony suspend in the special multicomponent environment and subject to flash in a combination with cooling and freezing. Freeze drying (see. Lyophilizing ) allows to keep viability of an essential part of population for a number of years and excludes selection.

For B.'s preservation to. on mediums use seeding for 0,6% nutrient agar in a column with addition of serum. At storage of auxotrophs on Wednesday it is necessary to add necessary growth factors. For protection from drying the grown cultures fill in from above with a sterile liquid paraffin or solder test tubes and store them at t ° — 4 °. It is recommended to carry out resowings of culture after check of the main properties at least once in 6 months. Storage on mediums at a temperature over 0 ° does not exclude division of bacteria. More frequent resowings are necessary for nek-ry species of bacteria. Spore-forming bacteria, on the contrary, can be stored without updating of the environment a long time.

The bacterial strains used in production and research store in the museums of live cultures at institutes and laboratories of the corresponding profiles. Exchange of bacterial strains between laboratories of various countries is organized.

An order of storage, the address, issue and B.'s accounting to. pathogenic microorganisms it is established by the corresponding instructions.

Bibliography: Meynell D. and Meynell E. Experimental microbiology, the lane with English, M., 1967, bibliogr.; The collection of techniques on genetics of microorganisms, under the editorship of R. Claus and U. Heys, lane with English, M., 1970, bibliop?.; T and m and-kov V. D. and D. M Goldfarb. Fundamentals of experimental medical bacteriology, M., 1958; Eksperimen talny microbiology, under the editorship of S. Byr-darov, the lane with bolg., Sofia, 1965, bibliogr.

S. S. Belokrysenko.

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