From Big Medical Encyclopedia

STRAINS of a vmikrobiologiya (German Stamm) — the cultures of microbes which are marked out from a certain source and identified according to tests of modern classification.

Distinguish reference, epidemic, atypical, the attenuirovanny (weakened) and virulent Sh. of microbes. The strains which are completely corresponding to the specific characteristic or possessing permanent changes of separate signs and applied to comparison with them of again marked out cultures are called reference, or referens-strains. Reference Sh. are collected in special international, national and industry referens-laboratories. The international collections Sh. of bacteria and viruses (including phages) are widely used for the genetic analysis (see Bacteria, the geneticist of bacteria). The strains allocated at epidemic flashes (so-called epidemic Sh.) quite often have the specific features distinguishing them from reference. Various strains of microbes of the same look can differ significantly from each other. E.g., the strains of Salmonella typhi possessing N = 0-and Vi-antigens, and also deprived of one or two of them are known; the cultures of bacteria corresponding to most resistant and widespread «phases» of dissociation (on old terminology the called S-, R-forms, etc.). Differing on cultural signs markedly, they keep the properties defining their specific characteristic (see Dissociation of a bacterium).

From natural substrates Sh. which do not have a full complex of the taxonomical signs corresponding to the characteristic of a certain species of microorganisms, so-called atypical strains are quite often allocated. Exact identification of atypical Sh. is important in medical microbiology for identification inf. the diseases caused by them.

For prevention inf. diseases the attenuirovanny (weakened) Sh. of the corresponding activators with firmness keeping an immunogenicity at falloff of virulence are used (see Vaccines). For the production purposes the most virulent Sh. having property to stimulate education specific (protective and diagnostic) antibodies in an organism of a sensitive animal in high credits biol are selected. activities and immunol. specificity.

For ensuring stability of properties of various Sh. it is necessary to create optimal conditions of their cultivation and storage taking into account biol. features.

See also Bacterial culture. of, Kudlay.