Lack of efficacy for conventional gamma irradiation of platelet concentrates to abrogate bacterial growth.

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Abstract
The maximum storage time for platelet concentrates is 5 days, owing to the higher risk bacterial contamination with longer storage. The expiration date could potentially be extended if a rapid system to detect microbial contamination or a safe sterilization technique could be developed and easily implemented. Gamma irradiation has decreased bacterial contamination in food products. Conventional doses of gamma irradiation were tested for their efficacy in decreasing bacterial growth during the 5-day platelet shelf life. An initial pilot study determined that bacteria suspended in normal saline at concentrations of 1 to 2 x 10(7) colony-forming units per milliliter showed a dose-related susceptibility to gamma irradiation. Subsequently, four platelet concentrates were pooled, inoculated with a known concentration of Staphylococcus autreus or Serratia marcescens, and divided. The concentrates were exposed to varying amounts of gamma irradiation, ie, no irradiation (control), 25, 50, and 75 Gy, and subjected to typical blood bank storage conditions. The platelet concentrates were sampled daily for 7 consecutive days to monitor bacterial growth by quantitative cultures. An inverse linear dose-related extinction of bacteria was evident in the pilot study with an extrapolated total kill in the 100 to 150 Gy range. There is no difference in bacterial growth with S aureus using irradiation 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 through 50 Gy. Exposure of bacteria-contaminated platelet concentrates on storage day zero to gamma irradiation at levels up to 75 Gy is ineffective at sterilizing the platelet concentrates. Higher levels of irradiation may be effective in sterilizing platelet concentrates. Function, survival, and sterility after higher than conventional levels of irradiation need further study.

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