The contribution of a number of extracellular products of to the virulence of the organism for mice was studied by comparing a wild-type strain with various mutants derived from it in three virulence tests: (1) subcutaneous and (2) intravenous challenge in normal mice, and (3) subcutaneous challenge in mice after total body X-irradiation.

Mutants with lower production or non-production of coagulase, staphylokinase and leucocidin were just as virulent for mice as the wild type in all three tests. Unlike the wild type, mutants with low production or non-production of α-lysin never gave necrosis after subcutaneous injection in normal mice. One mutant with loss of δ-lysin and unaltered α-lysin production gave necrosis only when injected in high doses. Dermonecrosis seems to be caused by a combination of α- and δ-lysin.

Intravenous injection of each of the two types of mutant in normal mice gave a lower mortality rate than that obtained with the wild type. Mutants with deficient α-lysin production, but not δ-lysin-deficient mutants, multiplied more slowly in the kidneys than the wild type under these conditions. α-Lysin appears to have a growth-enhancing effect for the organism , but δ-lysin does not.

Differences in virulence between the wild type and mutants could not be demonstrated in irradiated mice.


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