Virulence of coagulase-deficient mutants of Staphylococcus aureus in experimental endocarditis

Summary A sensitive rat endocarditis model which employed relatively small inocula (≤ 10‡ cfu) was used to examine the role of coagulase in the pathogenesis of infection. Rats with indwelling, intracardiac catheters were challenged intravenously with three strains of Staphylococcus aureus. The virulence of a coagulase-positive parental strain DU5808 was compared in terms of its ID50 for resected vegetations and catheters to that of two coagulase-negative mutant strains (DU5809 and DU5814) which had undergone site-specific muta-genesis. Confidence intervals of infection rates were calculated and comparisons were performed of weights of infected vegetations, bacterial concentrations in vegetations and early mortality rates. From these virulence parameters, it was concluded that there were no differences in virulence among the three strains. The results from this investigation support the previous findings in mouse models of subcutaneous infection and mastitis, which indicated that coagulase production by S. aureus does not appear to function as a virulence factor. Together, these data refute the longheld belief that coagulase is important in the pathogenesis of infection and indicate that other markers of virulence must be operative in diseases caused by the enduring pathogen S. aureus.