Evaluation of the lysis-centrifugation system for culturing dialysates from continuous ambulatory peritoneal dialysis patients with peritonitis.

Recovery of organisms from continuous ambulatory peritoneal dialysis (CAPD) patients with peritonitis presents special problems to the laboratory. The Isolator (Dupont Co, Wilmington, DE), based on lysis and centrifugation, is generally used for the recovery of blood isolates. This study determined the efficacy of the Isolator relative to the Bactec System (Johnston Laboratories, Inc, Towson, MD) for the culture of dialysates from CAPD patients with peritonitis. On the basis of clinical criteria, 31 episodes of peritonitis were included for our study. Dialysate was inoculated into an Isolator and Bactec 6B and 7D bottles. A causative agent was isolated by the Isolator in 29 of 31 episodes, by the Bactec in 29 of 31, and by one or both techniques in 30 of 31 episodes (overall sensitivity 97%). The Isolator failed to detect a Pseudomonas luteola and the Bactec failed to detect a coagulase-negative staphylococcus. Coagulase-positive and negative staphylococci represented 58.1% of the isolates. The Isolator detected 21.4% (six of 28) of the isolates 24 to 72 hours earlier than the Bactec; the Bactec was faster in this regard in 3.6% (one of 28). Time to positivity for the remaining 21 cultures was the same in both systems. Isolate identification and antimicrobial sensitivity was available 24 hours earlier using the Isolator in 96.4% (27 of 28). The Isolator was more rapid and as sensitive as the Bactec system in detecting causative organisms of peritonitis in CAPD patients.