Evaluation of an automated culture system for detecting bacterial contamination of platelets: an analysis with 15 contaminating organisms

BACKGROUND: Approximately 1 in 2000 platelet components are bacterially con taminated. The time to detection of 15 seeded organisms in platelets recove red from an automated culture system was studied. STUDY DESIGN AND METHODS: Isolates of Bacillus cereus, Bacillus subtilis, C andida albicans, Clostridium perfringens, Corynebacterium species, Enteroba cter cloacae, Escherichia coli, Klebsiella oxytoca, Propionibacterium acnes , Pseudomonas aeruginosa, Staphylococcus aureus, Staphylococcus epidermidis , Serratia marcescens, Streptococcus pyogenes, and Streptococcus viridans w ere inoculated into Day 2 apheresis platelet components to obtain a final c oncentration of approximately 10 and 100 CFU per mt (2 units/organism). Eac h bag was sampled 10 times (20 mL/sample). Four mt of each sample was inocu lated into standard aerobic and anaerobic bottles and into aerobic and anae robic bottles containing charcoal; 2 mt was inoculated into pediatric aerob ic bottles (so as to maintain a 1:10 ratio of sample to media) and 1 mt int o thioglycollate broth. RESULTS: With the exception of P.acnes, all organisms were detected in a me an of 9.2 to 25.6 hours. A range of 10 serial dilutions in inoculating conc entrations was associated with an overall 10.1-percent difference in detect ion time. A mean of 74.4 and 86.2 hours (100 and 10 CFU/ml inocula, respect ively) was required for the detection of Fl acnes in anaerobic bottles. CONCLUSION: Bacteria thought to be clinically significant platelet contamin ants can be detected in 9.2 to 25.6 hours when the starting concentration i s approximately 10 to 100 CFU per mt. Fl acnes required considerably longer incubation times for detection (in either aerobic or anaerobic bottles). H owever, Fl acnes is of questionable clinical significance. Such a detection system could be used in either a blood collection center or a transfusion service to screen platelet concentrates for bacterial contamination. Such t esting (with sterile sampling performed so as to maintain a closed-bag syst em) would be expected to save lives and might allow an extension of platele t storage.