Isolation and virulence of a caseinase- and bound coagulase-deficient mutant of Staphylococcus aureus BB

A caseinase - and bound coagulase-negative mutant was isolated from Staphylococcus aureus BB by treatment with N-methyl-N'-nitro-N-nitrosoguanidine. The virulence of the mutant strain was compared with that of the parental strain in mice infected by the intravenous and intraperitoneal routes. The ratio between the LD50 of the mutant and that of the parent was 1,841 for intravenous infection and 106 for intraperitoneal infection. Viable staphylococci were counted in renal tissue three days after intravenous infection with 3 X 10(6) bacteria; the count was 8 X 10(7) cfu/100 mg of tissue for the parental strain and 1.2 X 10(2) cfu/100 mg for the mutant strain.