Transfusion‐transmitted bacterial infection risk due to the proliferation of psychrotrophic bacterial species in RBCs and their difficulty in detection

Abstract Background Reports of cases of bacterial infection due to transfusion of red blood cell (RBC) components (RBC‐TTBI) are relatively rare. Hence, the possibility of undetectable bacterial contamination in RBCs, especially by psychrotrophic bacteria, must be clarified. Study Design and Methods We assessed nine psychrotrophic bacterial species, including those implicated in bacteremia or RBC‐TTBIs. They were cultured on plates from 4 to 37°C to determine their optimal growth temperatures. We also assessed the detection capabilities of the automated culture/alarm system BACT/ALERT VIRTUO (VIRTUO) using BPA (aerobic) and BPN (anaerobic) bottles. In addition, bacteria‐inoculated RBCs were incubated at 4°C for 42 days, with samples assessed weekly for bacterial growth using plate culture, VIRTUO, visual inspection, and endotoxin production. Results Two Psychrobacter species exhibited weak or no proliferation at temperatures ≥30°C in plate cultures. Three Pseudomonas species, one Psychrobacter species, and one psychrotrophic lactic acid bacteria proliferated in RBCs at 4°C, reaching 10 4 –10 8 colony‐forming units/mL (growth count) and 15–39,230 pg/mL (endotoxin production) by day 14. VIRTUO, operating at 36°C, failed to consistently yield reliable results for any of the tested bacterial species. Notably, visual changes in bag appearance were observed from day 21 in four species that proliferated in RBCs. Discussion Each psychrotrophic bacteria demonstrated a specific temperature preference for optimal proliferation. Standard culture tests, typically conducted at 35–37°C, often fail to detect the growth of such bacteria, suggesting they may be overlooked in the cultural analysis of suspected RBC‐TTBI cases.