Comparative virulence of human isolates of coagulase-negative staphylococci tested in an infant mouse weight retardation model.

Human infections caused by coagulase-negative staphylococci have steadily increased in numbers and severity. Causes may be the use of artificial prostheses, immunocompromising chemotherapy and radiation therapy, and sophisticated surgical techniques, to name a few. Although the infectivity of coagulase-negative staphylococci as a group has been well documented for humans, attempts to study the pathogenesis of infections caused by individual species of coagulase-negative staphylococci have been hampered by the lack of an animal model that is not refractory to infection by these organisms. In the study reported here, a 2-day-old-mouse weight retardation test was used to assay the virulence of 60 clinical and reference strains of coagulase-negative staphylococci. These strains represented eight species of coagulase-negative staphylococci. The most virulent strains were demonstrated to be of the species Staphylococcus haemolyticus, S. saprophyticus, and S. epidermidis. The data further suggest that production of slime is a marker of virulence in S. epidermidis and that intraspecies differences in virulence occur.