ABSTRACT
BACKGROUND AND OBJECTIVES: Platelet concentrates (PC) are stored at 20-24°C to maintain platelet functionality, which may promote growth of contaminant bacteria. Alternatively, cold storage of PC limits bacterial growth; however, data related to proliferation of psychotrophic species in cold-stored PC (CSP) are scarce, which is addressed in this study. MATERIALS AND METHODS: Eight laboratories participated in this study with a pool/split approach. Two split PC units were spiked with ~25 colony forming units (CFU)/PC of Staphylococcus aureus, Klebsiella pneumoniae, Serratia liquefaciens, Pseudomonas fluorescens and Listeria monocytogenes. One unit was stored under agitation at 20-24°C/7 days while the second was stored at 1-6°C/no agitation for 21 days. PC were sampled periodically to determine bacterial loads. Five laboratories repeated the study with PC inoculated with lyophilized inocula (~30 CFU/mL) of S. aureus and K. pneumoniae. RESULTS: All species proliferated in PC stored at 20-24°C, reaching concentrations of ≤109 CFU/mL by day 7. Psychrotrophic P. fluorescens and S. liquefaciens proliferated in CSP to ~106 CFU/mL and ~105 CFU/mL on days 10 and 17 of storage, respectively, followed by L. monocytogenes, which reached ~102 CFU/mL on day 21. S. aureus and K. pneumoniae did not grow in CSP. CONCLUSION: Psychrotrophic bacteria, which are relatively rare contaminants in PC, proliferated in CSP, with P. fluorescens reaching clinically significant levels (≥105 CFU/mL) before day 14 of storage. Cold storage reduces bacterial risk of PC to levels comparable with RBC units. Safety of CSP could be further improved by implementing bacterial detection systems or pathogen reduction technologies if storage is beyond 10 days.
ABSTRACT
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.
