Platelet Metabolism during Room Temperature Storage Contributes to Bacterial Growth: Effect Mitigated By Refrigeration

Introduction: Transfusion related sepsis is a serious concern limiting platelet storage time to 5 days at room temperature. While most units are screened for bacterial contamination when collected, most bacterial monitoring methods can take up to 7 days to detect potential contamination. Thus, cold storage of platelets represents an attractive alternative for improving platelet safety. In this study, we assessed bacterial growth in platelets stored either at room temperature (22^oC) or refrigerated (4^oC).

Methods: Apheresis platelets in plasma (PLT) were obtained from healthy donors using the Terumo Trima Accel Automated Blood Collection System (Terumo BCT). Fresh plasma (FP) was collected similarly. Aliquots of PLT or FP were transferred to pH SAFE minibags (Blood Cell Storage, Inc) and inoculated with Acinetobacter baumannii, Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Staphylococcus epidermidis, or PBS (uninfected control). Minibag aliquots stored at RT were agitated using an orbital shaker set to 60 rpm while refrigerated aliquots were stored under static conditions. Bacterial growth was monitored daily through dilution plating. Lactate levels in PLT aliquots were assessed by iSTAT (Abbott) using CG4+ test cartridges while plasma glucose levels were assessed using blood glucose testing strips (Germaine Laboratories). Platelet activation and aggregation were assessed on days 0, 1, 3, and 5 by flow cytometry and Multiplate platelet aggregometry, respectively.

Results: Bacterial growth progressed rapidly over the first 3-4 days post-collection in all PLT aliquots stored at RT except those challenged with S. epidermidis. Significant growth of S. epidermidis was not detected until day 4. No change in bacterial numbers were detected in any refrigerated aliquots through day 5. While refrigeration appeared to preserve PLT function throughout with low levels of activation irrespective of bacterial contamination, RT storage resulted in significantly (p < 0.05) decreased platelet aggregation over time which was exacerbated by bacterial contamination. In the absence of metabolically active PLTs, bacterial growth was significantly reduced, or at least delayed, in all test groups. FP aliquots challenged with Gram-negative pathogens exhibited a significant (p < 0.05) delay in bacterial growth at day 1. While growth of E. coli and P. aeruginosa recovered by day 2, growth was significantly (p < 0.05) inhibited in aliquots challenged with A. baumannii throughout the observation period. Conversely, no differences in bacteria growth were observed in aliquots challenged with Gram-positive pathogens until day 3, at which point growth appeared to be significantly (p< 0.05) stunted in FP relative to PLT aliquots. Bacterial growth appeared to correlate with PLT lactate production. However, only E. coli showed clear signs of lactate utilization as lactate levels diminished significantly after day 3. Despite this, A. baumannii, E. coli, and S. epidermidis, exhibited increased bacterial growth in FP aliquots supplemented with concentrations of lactic acid in excess of 15 mM.

Conclusions: Bacterial growth, platelet activation and platelet lactate production appeared largely static throughout in refrigerated aliquots. Conversely, bacterial growth was significantly increased in all RT stored aliquots, as was lactate production suggesting platelet metabolism may contribute to bacterial growth. Illustrating this, lactic acid concentrations in excess of 15 mM modulated growth of A. baumannii, E. coli, S. epidermidis in FP. These data demonstrate that bacterial growth can be controlled through refrigeration without loss of function and RT storage may potentiate growth of certain bacterial strains through accelerated PLT metabolism.