Establishment of transfusion-relevant bacteria reference strains for red blood cells.

BACKGROUND AND OBJECTIVES: Red blood cell concentrates (RBCC) are susceptible to bacterial contamination despite cold storage. A reliable evaluation of strategies to minimize the risk of RBCC-associated bacterial transmission requires the use of suitable reference bacteria. Already existing Transfusion-Relevant Bacteria Reference Strains (TRBRS) for platelet concentrates fail to grow in RBCC. Consequently, the ISBT TTID, Working Party, Bacterial Subgroup, conducted an international study on TRBRS for RBCC. MATERIALS AND METHODS: Six bacterial strains (Listeria monocytogenes PEI-A-199, Serratia liquefaciens PEI-A-184, Serratia marcescens PEI-B-P-56, Pseudomonas fluorescens PEI-B-P-77, Yersinia enterocolitica PEI-A-105, Yersinia enterocolitica PEI-A-176) were distributed to 15 laboratories worldwide for enumeration, identification, and determination of growth kinetics in RBCC at days 7, 14, 21, 28, 35 and 42 of storage after low-count spiking (10-25 CFU/RBCC). RESULTS: Bacterial proliferation in RBCC was obtained for most strains, except for S. marcescens, which grew only at 4 of 15 laboratories. S. liquefaciens, S. marcescens, P. fluorescens and the two Y. enterocolitica strains reached the stationary phase between days 14 and 21 of RBCC storage with a bacterial concentration of approximately 109  CFU/ml. L. monocytogenes displayed slower growth kinetics reaching 106 -107  CFU/ml after 42 days. CONCLUSION: The results illustrate the importance of conducting comprehensive studies to establish well-characterized reference strains, which can be a tool to assess strategies and methods used to ameliorate blood safety. The WHO Expert Committee on Biological Standardization adopted the five successful strains as official RBCC reference strains. Our study also highlights the relevance of visual inspection to interdict contaminated RBC units.

Extending the 30-minute rule for red cell units - investigation of the bacterial risk of 60-minute exposures to ambient temperature.

BACKGROUND AND OBJECTIVES: In the UK, a significant proportion of red cell units is discarded due to the 30-min rule governing out of temperature control. Studies have shown that repeated warming to ambient temperature has little impact on red cell quality or bacterial growth. We aimed to validate extension of the rule to 60 minutes by investigation of repeated same, and different, day exposures on bacterial growth. MATERIALS AND METHODS: Red cell units were seeded individually at 100-1000 cfu/ml with Yersinia enterocolitica, Serratia liquefaciens, Pseudomonas putida, Staphylococcus epidermidis, Enterobacter cloacae and Bacillus cereus. Test units were exposed to 30°C for 30 or 60 min on a single occasion at days 15, 17 and 21, or thrice on day 15 of a 35-day storage period. A 10-fold increase in bacterial counts in tests versus controls maintained in cold storage was considered indicative of significant bacterial proliferation. RESULTS: Exposure of units to 30°C for up to 60 min had no substantial impact on the growth of bacteria and all mesophiles declined steadily in tests and controls. Only P. putida showed a near significant elevation in count on exposure for 60 min at day 35. CONCLUSIONS: Extension of the out of temperature rule for red cells to 60 min will potentially not compromise patient safety, although exposures to ambient temperatures should be minimized. Units returned to storage must not be reissued for at least 6 hours and not be exposed to ambient temperatures on more than three occasions.