Platelets Feeding Bacteria with Lactate during Room Temperature Storage: Mitigated By Refrigeration

Introduction: Platelet transfusion related sepsis is a serious concern limiting platelet storage time to 5 days. Room temperature (RT) storage of platelets increases the risk of bacterial growth and necessitates implementation of bacterial contamination monitoring. 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). Platelet poor plasma (PPP) was obtained from PLT aliquots centrifuged twice at 2,500 x g for 5 min. In some experiments aliquots of PPP were supplemented with 5 to 20 mM lactic acid. Aliquots of PLT or PPP were transferred to pH SAFE minibags (Blood Cell Storage, Inc) and inoculated with Acinetobacter baumannii strains Ci77 or Ci79, Escherichia coli, Pseudomonas aeruginosa, 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. Platelet activation and aggregation were assessed on days 0, 1, 3, and 5 by flow cytometry and Multiplate platelet aggregometry respectively.

Results: Growth of A. baumannii progressed exponentially over the first 3 days post-collection in PLT aliquots stored at RT. However, growth was significantly (p < 0.05) reduced in PPP units. Growth of E. coli and P. aeruginosa, both of which are capable of utilizing glucose present in the anticoagulant used, grew at significantly faster rates and did not seem to be dependent on metabolically active PLTs. Lactate levels were assessed in PLT units and found to mirror growth of A. baumannii . Furthermore, addition of ≥ 15 mM lactic acid to RT stored PPP restored A. baumannii growth. Although lactate levels did not appear to contribute to growth of E. coli, lactate levels began to decrease in PLT units contaminated with the bacterium at a rapid rate after day 3. Lactate levels in units contaminated with P. aeruginosa increased throughout the observation window. Bacterial growth remained static throughout under all treatment conditions stored refrigerated and lactate levels were reduced. PLT also appeared to retain function throughout cold storage irrespective of bacterial contamination while RT storage resulted in a decrease in aggregation over time which was exacerbated by bacterial contamination.

Conclusions: Bacterial growth remained static throughout under cold storage. Additionally, PLT lactate production was increased at RT and correlated with increased growth of A. baumannii . Growth of E. coli and P. aerugionsa appeared to proceed independently of lactate production or metabolically active PLTs. However, E. coli did appear to utilize lactate as a carbon source at later time points. These data demonstrate that bacterial growth can be controlled through refrigeration without loss of function and RT stored platelets may potentiate growth of certain bacterial strains through accelerated metabolism relative to cold storage.