Growth of Streptonigrin-Resistant Staphylococcus epidermidis with Defective Siderophore-Mediated Iron-Uptake System in Human Peritoneal Dialysate Solution

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.

Growth of Streptonigrin-Resistant Staphylococcus epidermidis with Defective Siderophore-Mediated Iron-Uptake System in Human Peritoneal Dialysate Solution

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.

Utilization of Transferrin-Bound Iron by Medically Important Staphylococcal Species

Staphylococcus aureus is able to utilize efficiently transferrin-bound iron as an iron source, whereas other staphylococci are not. The reason for this difference remains unclear. We compared the activity of siderophore-mediated iron-uptake systems among S. aureus, S. epidermidis, and S. saprophyticus. S. aureus was more susceptible to streptonigrin than the other two staphylococci. S. aureus was able to utilize efficiently transferrin-bound iron in proportion to the level of iron-saturation and produced siderophores in an inverse relation to iron-saturation. In contrast to S. aureus, S. epidermidis and S. saprophyticus were able to utilize only holotransferrin (HT; about 80% iron- saturated) and produced siderophores only in media containing HT. Moreover, they utilized HT less efficiently than S. aureus, though they produced greater amount of siderophores than S. aureus in media containing HT. The ability of the equivalent siderophores per se to capture iron from HT was not significantly different among the three species. Nevertheless, the siderophores from S. aureus stimulated the growth of the staphylococci to a greater degree than did the siderophores from S. epidermidis and S. saprophyticus. The siderophores from S. epidermidis and S. saprophyticus also stimulated the growth of S. aureus to a greater degree than those of the original bacteria which produced them. This indicates that S. aureus possesses a greater ability to produce more-efficient siderophores responding to very low iron-availability, as well as a greater ability to utilize iron-siderophore complexes, than the other two staphylococci. This explains in part the higher virulence of S. aureus compared to other staphylococci.

Bacterial Growth in Amniotic Fluid Is Dependent on the Iron-Availability and the Activity of Bacterial Iron-Uptake System

In the present study, the relationship among iron-availability, antibacterial activity, role of meconium as an iron source and the activity of bacterial iron-uptake system (IUS) for bacterial growth in amniotic fluid (AF) were investigated. Staphylococcus aureus ATCC 6538 and its streptonigrin-resistant (SR) mutant with defective IUS were used as the test strains. The growth of S. aureus in AF was stimulated dosedependently by addition of meconium. Bacterial growth stimulated by meconium was re-inhibited dose-dependently by addition of iron-chelator, dipyridyl and apotransferrin. Iron concentration was correlated with the meconium content in AF (r(2)= 0.989, p=0.001). High-affinity IUS of S. aureus was expressed only in AF but not in AF with meconium. The growth of SR strain was more retarded than that of the parental strain in the iron-deficient brain heart infusion (ID-BHI), clear AF and AF containing apotransferrin. The retarded growth of both strains in the ID-BHI and AF was recovered by addition of holotransferrin, hemoglobin and FeCl3. Taken together, the antibacterial activity of AF is closely related with low iron-availability. Bacterial growth in AF considerably depends on the activity of bacterial IUS. Meconium acts as one of the exogenous iron-sources and thus can stimulate bacterial growth in AF.