Influence of Coagulases and Route of Injection on Staphylococcal Virulence in Mice.

Abstract

The median lethal dose (LD50) of each of 12 strains of staphylococci, representing typical coagulase positive Staphvlococcus aureus and variants which lack either coagulase or clumping factor (bound coagulase) or both these properties, was determined by intravenous and intraperitoneal injection of washed cells into albino mice. Intraperitoneal challenge compared saline and mucin suspensions of the cells. Results indicated that neither coagulase nor clumping factor, per se, was a critical factor of virulence for mice. Comparison of LD50 values of strains grouped according to coagulase and clumping factor indicated there was an interaction between route of injection, group and virulence. Saline suspended, coagulase positive staphylococci which lacked clumping factor were, as agroup, slightly more virulent by intraperitoneal route than by intravenous route. Mucin markedly enhanced the intraperitoneal virulence of these organisms but not that of other strains. By the intraperitoneal route mucin suspended, coagulase positive, clumping factor negative staphylococci were the most virulent organisms tested regardless of coagulase titer.