Determination of differences in virulence of strains of Salmonella typhosa; a comparison of methods.

An investigation is reported of a comparison by three methods of the degree and certainty of differentiation of strains of S. typhosa of different virulence for mice. These methods were (a) intracerebral injection, (b) intraperitoneal injection of saline suspensions, and (c) intraperitoneal injection of mucin suspensions of the test organisms. With the strains of S. typhosa employed, differentiation was questionable by the intracerebral method, somewhat more marked by the intraperitoneal-saline suspension method, and most definite by the intraperitoneal-mucin suspension method. Differentiation of the strains employed was found to be independent of the presence or absence of Vi antigen and apparently was more dependent upon the method of testing than upon any known differences in biological characteristics of the organisms.