Comparison of BACTEC versus conventional enrichment medium for peritoneal dialysate fluid culture

Abstract

Background: Bacterial peritonitis remains a significant cause of mortality in patients on peritoneal dialysis (PD). Early detection of causative organisms and targeted antimicrobial treatment allow for better clinical outcomes. This study compares bacterial growth results from peritoneal dialysate in the BACTEC blood culture system vs. conventional culture.

Materials and methods: We conducted a prospective study on 46 patients with 63 consecutive episodes of suspected PD peritonitis between August 2020 and August 2021. PD dialysate was simultaneously sent to the laboratory in both BACTEC and sterile bottles. BACTEC bottles were incubated in the BD BACTEC FX system for 5 days. PD effluent transported from the sterile bottles was centrifuged at 3,000 rpm for 15 minutes; the supernatant was inoculated into cooked-meat broth for enrichment. Both incubation methods were extended to 14 days if microorganisms were seen on the Gram-stained smear. Recovery of isolated micro-organisms and time to detection (TTD) were compared.

Results: 26 episodes of suspected PD peritonitis based on clinical criteria were identified during the study period. The sensitivity of the BACTEC and the conventional culture methods was 50% and 42.3%, respectively (p = 0.45). Seven samples had partial concordance or discordant results. McNemar's χ²-test revealed no statistical difference between either method (p = 0.45). TTD was 18.9 ± 24.4 hours via the BACTEC method vs. 37 ± 16.5 hours in conventional cultures (p = 0.014).

Conclusion: The comparable sensitivities and similar yield in identifying pathogens could be due to the enrichment medium and prolonged incubation period. The shorter TTD for the BACTEC method could facilitate earlier confirmation of bacteriological diagnosis and subsequent treatment strategies.