VARIATION IN THE EXPRESSION OF CELL-ENVELOPE PROTEINS OF COAGULASE-NEGATIVE STAPHYLOCOCCI CULTURED UNDER IRON-RESTRICTED CONDITIONS IN HUMAN PERITONEAL DIALYSATE

Strains of coagulase-negative staphylococci (CNS), including Staphylococcus epidermidis, S. hominis, S. warnerii, S. simulans, S. capitis, S. haemolyticus and S. saprophyticus, were isolated from patients with continuous-ambulatory-peritoneal-dialysis-related peritonitis. The cell wall and cytoplasmic membrane protein profiles of CNS strains cultured in either nutrient broth (NB) or pooled human peritoneal dialysate (HPD) were compared. Some interspecies variation in both the wall and membrane protein profiles was noted. However, the cell wall protein profiles of HPD-grown CNS strains differed markedly from those cultured in NB. Growth in HPD resulted in a marked reduction in the total number of cell-wall-associated proteins but up to three antigenically related proteins in the 40-56 kDa range, depending on the species, predominated. Growth in HPD also resulted in the induction of two iron-repressible cytoplasmic membrane proteins (IRMPs) of 32 and 36 kDa in S. epidermidis. Other CNS strains only appeared to express a single IRMP, which varied in molecular mass from 32 to 36 kDa. Whilst the IRMP in these CNS strains showed considerable antigenic homology with the 32 kDa IRMP, the S. warneri IRMP showed cross-reactivity with both the 32 and 36 kDa IRMPs of S. epidermidis. Immunoblotting experiments revealed that whilst the CNS cell wall proteins were poorly immunogenic, the IRMPs were the immunodominant CNS protein antigens, reacting strongly with antibodies present in HPD. This finding provides evidence to suggest that the IRMPs are expressed in vivo during infection.