In-house validation of the BACTEC 9240 blood culture system for detection of bacterial contamination in platelet concentrates.

ABSTRACT

BACKGROUND: At present, only two commercially available automated culture systems are cleared by the FDA for the purpose of quality control (QC) testing for bacterial contamination of platelet (PLT) concentrates the BacT/ALERT blood culture system (bioMérieux) and the Pall eBDS (Pall Corporation), both of which allow testing of leukoreduced apheresis as well as whole blood-derived PLTs. After the decision of the AABB to institute universal QC testing of PLT concentrates for evidence of bacterial contamination, in-house validation of the performance of our current blood culture system, the BACTEC 9240, was carried out for this purpose. STUDY DESIGN AND METHODS: Serial dilutions of nine species of bacteria commonly associated with PLT contamination were prepared in one single-donor apheresis PLT unit per organism. Four mL of dilutions containing less than 1 to greater than 10(3) colony-forming units (CFUs) per mL was inoculated into blood culture bottles (Standard 10 Aerobic/F, Becton-Dickinson Diagnostic Systems) and incubated in a BACTEC 9240 continuously monitored blood culture system. Positive bottles were removed from the system and subcultured to insure the identity of bacterial growth. RESULTS: With the exception of Streptococcus mitis, the BACTEC system provided a detection sensitivity of less than 10 CFUs per mL for Staphylococcus aureus, Staphylococcus epidermidis, Escherichia coli, Serratia marcescens, Klebsiella pneumoniae, Bacillus cereus, Enterobacter cloacae, and Pseudomonas aeruginosa. The limit of detection for the S. mitis test strain was 61 CFUs per mL. Detection of positive bottles ranged from 6.5 to 17.6 hours depending on the species tested and the cell density of the inoculum. Ongoing use of this system for bacterial detection yielded two true-positive samples from 3879 apheresis PLT products collected at our hospital-based donor center over 9 months. CONCLUSION: This study validates the use of the BACTEC 9240 continuously monitored blood culture system for the detection of low-level bacterial contamination in single donor apheresis PLTs in less than 24 hours.