Virulence of genus Staphylococcus. III. Studies on the pathogenicity to mice.

Six representative strains of staphylococci were selected on the basis of DNase activity and inoculated into the mice to study the correlation of the presence of this enzyme to the virulence of the staphylococci. Two strains of staphylococci among them produced DNase but not the free coagulase, and one of these two strains had an obvious virulence against the mice. The results of experiments suggest that there are at least certain strains which may be designated as Staphylococcus aureus among these DNase-producing staphylococci producing no free coagulase. This is an additional evidence that this enzyme activity should be adopted as a criterion to distinguish from the other S. aureus which has lost the free coagulase activity. In this sense, the staphylococci producing neither free coagulase nor DNase are after all Staphylococcus epidermidis, regardless of their ability to ferment mannitol or not.