Comparison of Microbiologic Characteristics of Pathogenic and Saprophytic Coagulase-negative Staphylococci from Patients on Continuous Ambulatory Peritoneal Dialysis

Twenty-one microbiologically documented episodes of coagulase-negative staphylococcal peritonitis occurred in 21 continuous ambulatory peritoneal dialysis patients. All strains involved in these infections were tested for antimicrobial susceptibility and in vitro adherence assays. Twenty of the strains were species identified using two commercially available systems. For comparison, 20 saprophytic strains of coagulase-negative staphylococci obtained from the nares and axillae of 10 uninfected, peritoneal dialysis patients were included for in vitro characterization. Staphylococcus epidermidis was the species most often identified for both clinical and saprophytic strains. Eighteen of the 21 (86%) clinical strains were resistant to penicillin G. Methicillin resistance, which was present in five clinical strains, was not found in saprophytic strains. Adherence assay determinations showed marked differences between clinical versus colonization strains, with the clinical isolates significantly more adherent (p less than 0.025) than colonization strains. Electron microscopic examination of silastic catheter segments incubated with a strain of S. epidermidis in used and unused dialysis fluids demonstrated marked differences in attachment of bacteria to catheter material.