Rapid detection of bacterial contamination of platelet-rich plasma-derived platelet concentrates using flow cytometry

Flow cytometry can be used to detect bacterial contamination of platelet products. In this study, we investigated whether the incubation of a minimal volume of platelet-rich plasma (PRP)-derived platelet concentrates (PCs) with growth medium improved the analytical sensitivity of flow cytometry. Five bacterial strains (Staphylococcus aureus, Staphylococcus epidermidis, Bacillus cereus, Klebsiella pneumoniae, and Escherichia coli) were used. Platelets were inoculated with 10, 10(2), and 10(3) CFUs per mL; 0.5 mL, 1.0 mL, and 2.0 mL aliquots of spiked platelets were incubated with growth medium at 37°C for 24 hours. During the incubation period, the numbers of events were analyzed every 4 hours by flow cytometry. We could detect a low concentration (10 CFUs per mL) of bacteria in a small volume (minimum 0.5 mL) of PCs. Irrespective of spiking concentrations and incubation volumes, the detection times of S. aureus and S. epidermidis were 24 hours or less, while those of B. cereus, K. pneumoniae, and E. coli were 16 hours or less. A higher spiking concentration made it possible to shorten the detection time. The numbers of detected bacteria increased during the incubation. However, the graphs corresponding to K. pneumoniae and E. coli showed peak levels and decreasing patterns during the incubation period. The incubation of small volumes of PC with growth medium increased the analytical sensitivity of flow cytometry for bacterial detection. Therefore, flow cytometry can serve as a useful method for sterility testing using PRP-derived PCs with only low levels of consequent platelet loss.