Significance of chromogenic variants in studies of virulence factors of Staphylococcus aureus.

Parisi, Joseph T. (Duquesne University, Pittsburgh, Pa.). Significance of chromogenic variants in studies of virulence factors of Staphylococcus aureus. J. Bacteriol. 92:589-591. 1966.-Large numbers of chromogenic variants were isolated from cultures of a parent strain of Staphylococcus aureus growing in Brain Heart Infusion (Difco). The parent strain and four selected chromogenic variants were tested for either quantitative or qualitative differences in the production of extracellular substances associated with virulence. Quantitative differences were found in the ability of these strains to produce coagulase and hyaluronidase, whereas qualitative differences were found in the production of plate hemolysins, bound coagulase, opacity in an egg yolk medium, and a proteinase. In view of the rate and extent of the occurrence of these chromogenic variants, their presence in an inoculum could lead to inaccurate results in in vitro studies of staphylococcal virulence.