LACK OF EFFICACY FOR CONVENTIONAL GAMMA-IRRADIATION OF PLATELET CONCENTRATES TO ABROGATE BACTERIAL-GROWTH

The maximum storage time for platelet concentrates is 5 days, owing to the higher risk bacterial contamination with longer storage. The expi ration date could potentially be extended if a rapid system to detect microbial contamination or a safe sterilization technique could be dev eloped and easily implemented. Gamma irradiation has decreased bacteri al contamination in food products. Conventional doses of gamma irradia tion were tested for their efficacy in decreasing bacterial growth dur ing the 5-day platelet shelf life. An initial pilot study determined t hat bacteria suspended in normal saline at concentrations of 1 to 2 x 10(7) colony-forming units per milliliter showed a dose-related suscep tibility to gamma irradiation. Subsequently, four platelet concentrate s were pooled, inoculated with a known concentration of Staphylococcus aureus or Serratia marcescens, and divided. The concentrates were exp osed to varying amounts of gamma irradiation, ie, no irradiation (cont rol), 25, 50, and 75 Gy, and subjected to typical blood bank storage c onditions. The platelet concentrates were sampled daily for 7 consecut ive days to monitor bacterial growth by quantitative cultures. An inve rse linear dose-related extinction of bacteria was evident in the pilo t study with an extrapolated total kill in the 100 to 150 Gy range. Th ere is no difference in bacterial growth with S aureus using irradiati on levels from 0 to 75 Gy. A 1-day delay in bacterial growth at 75 Gy was found with S marcescens compared with units irradiated with 0 thro ugh 50 Gy. Exposure of bacteria-contaminated platelet concentrates on storage day zero to gamma irradiation at levels up to 75 Gy is ineffec tive at sterilizing the platelet concentrates. Higher levels of irradi ation may be effective in sterilizing platelet concentrates. Function, survival, and sterility after higher than conventional levels of irra diation need further study.