BACKGROUND: Staphylococcus epidermidis is the most common pathogen of chronic ambulatory peritoneal dialysis peritonitis. It has been believed that the activity of iron-uptake system (IUS) may play an important role in the growth of S. epidermidis in human peritoneal dialysate (HPD) solution, but there is no report using mutants with defective IUS. A streptonigrin-resistant S. epidermidis (SRSE) strain was isolated from S. epidermidis KCTC 1917 and functionally characterized. MATERIALS AND METHODS: Bacterial growth was monitored by measuring the optical densities of culture fluids obtained at appropriate intervals at a wavelength of 600 nm. CAS agar diffusion assay was used for the comparison of siderophore production, 6 M urea-gel electrophoresis for the comparison of the ability to capture iron from transferrin, and bioassay for the observation of the ability to utilize iron-siderophore complexes. RESULTS: The SRSE strain ineffectively utilized transferrin-bound iron for growth despite its ability to produce considerably larger amount of siderophores than its parental strain. The growth of the parental strain, but not the SRSE strain, was stimulated on transferrin-bound iron by its own siderophores each. The growth of the SRSE strain in the HPD solution was retarded compared to that of the parental strain. CONCLUSION: These results indicate that the SRSE strain is defective in its ability to utilize the iron-siderophore complexes, rather than its ability to produce siderophores, and that the siderophore-mediated IUS plays an important role in the growth of S. epidermidis in HPD solution.