Opsonic requirements of Staphylococcus epidermidis.

The opsonic requirements of 18 strains of Staphylococcus epidermidis were compared in pooled normal human serum and in peritoneal dialysate from patients undergoing continuous ambulatory peritoneal dialysis (CAPD). A serum concentration of 2.5% gave optimal opsonisation. The opsonisation of all strains was antibody- and complement-dependent, and there were no significant differences in the pattern of their opsonic requirements. Peritoneal-dialysis effluent from uninfected patients was a poor source of opsonins because of the low levels of immunoglobulin G and of the C3 component of complement it contained. Growth of S. epidermidis in peritoneal-dialysis effluent rather than in broth did not alter its opsonic requirements. Strains from patients undergoing CAPD and suffering from peritonitis were not more resistant to opsonisation and phagocytic killing than those from other sources.