In vitro study of bacterial growth in continuous ambulatory peritoneal dialysis fluids

We examined the in vitro survival of bacteria in continuous ambulatory peritoneal dialysis effluents of patients with clinical peritonitis and those without peritonitis. Standard strains of coagulase-negative staphylococci (CNS), Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa were inoculated into the fluids, and portions were plated for bacterial counts at 0.5, 4, 24, 48, 72, and 96 h. Unused dialysate fluid was also inoculated simultaneously. Our results show that CNS increased minimally up to 48 h in the noninfected continuous ambulatory peritoneal dialysis effluents and decreased by 96 h, whereas survival was only minimal in the infected effluent. S. aureus showed trends similar to those of CNS, but differences in survival in infected and noninfected effluents were less marked. By contrast, E. coli and P. aeruginosa increased by greater than 1,000-fold in all solutions tested. Based on the above findings, it is likely that a proportionate number of culture-negative cases of peritonitis are due to gram-positive cocci, especially CNS, which are not retrievable by standard culture techniques because of poor survival rate.