Strains

Strains, a term used in microbiology for distinguishing cultures of microbes or samples of virus of the same name, with identical or different properties, but differing in origin. Strains are classified as original, passaged, local, and international. Original strains represent the initial strains, directly isolated from the organism or external environment. For longer preservation of the original strain, it undergoes passaging on artificial nutrient media or on suitable species of animals. As a result of passaging, the strain may lose some properties or acquire new ones. Local strains refer to strains isolated at the site of an epidemic outbreak. Local strains are advisable for use in preparing vaccines to be applied in the same locality where the strain was isolated, as well as in serodiagnostic tests there, since local strains are often more sensitive. International strains are either strains rarely isolated and therefore distributed to different countries, such as the Proteus X₁₉ strain, isolated by Weil and Felix in 1916, or strains possessing particularly pronounced properties, such as the toxigenic strain of diphtheria bacillus, named 'Park-Williams bacillus № 8', isolated in New York in 1894 and still used in all countries for obtaining diphtheria toxin. Special significance is attached to strain-vaccine (strain-lymph). This is the vaccine that is inoculated into cows for the purpose of obtaining material from them for inoculation into humans. This vaccine is also called maternal vaccine, or maternal detritus (see Smallpox detritus).