COMPARATIVE VIRULENCE OF STAPHYLOCOCCUS-EPIDERMIDIS ISOLATES IN A MURINE CATHETER MODEL

Among coagulase-negative staphylococci, Staphylococcus epidermidis is the species most commonly implicated in catheter-related infections. W hether some staphylococcal organisms are inherently more virulent than others, or whether their ability to infect relates more to the sheer numbers of organisms at the catheter site, remains unclear. We therefo re compared eight S. epidermidis isolates and two other coagulase-nega tive staphylococci using a murine model that allowed us to quantify ca theter colonization and abscess formation in the same animal. The orga nisms were isolated from different clinically relevant settings and we re classified according to their slime phenotype. The ability to evoke abscesses or colonize catheters in half of the animals (ID50) was ass essed. ID50 inoculum titers (log(10) data +/- SD) ranged widely, from 8.5 +/- 0.3 to 10.2 +/- 0.2 for abscess formation (p < 0.005) and from 7.5 +/- 0.5 to 10.3 +/- 1.0 for catheter colonization (p < 0.005). ID 50 values by statistical criteria suggested variability among organism s in the ability to induce abscess formation. High slime production co rrelated with both parameters, but not with the clinical source of the isolate. Our findings demonstrate impressive heterogeneity in the abi lity of a representative group of S. epidermidis isolates to colonize catheters and to evoke abscess formation and implicate slime productiv ity as a major virulence factor. The murine model used permitted simul taneous analysis of multiple factors involved in pathogenesis and shou ld be useful in establishing the basis of S. epidermidis pathogenicity .