Growth of gram‐positive and gram‐negative bacteria in platelet concentrates

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Abstract
In 1986 the allowable platelet storage time was reduced from 7 to 5 days because of a recent increase in septic deaths associated with platelet transfusion. In this study, the growth curves of two gram-positive and two gram-negative organisms in platelets stored for 7 days in CLX and PL-732 bags were evaluated. Platelets in CLX bags were inoculated with 101, 102, and 103 organisms and 102 organisms were introduced into PL-732 bags. Test organisms were inoculated into trypticase soy broth as a control. All four bacteria grew rapidly in trypticase soy broth, reaching 109 organisms per mL within 48 hours. In both CLX and PL-732 bags, the growth pattern of gram-positive organisms was generally logarithmic during the first few days of storage. A concentration of 108 organisms per mL was present by Day 3 or 4, after which further proliferation was inhibited by the high density of bacteria in the platelets. In PL-732 bags, the proliferation of gram-negative organisms followed a pattern similar to that of the gram-positive bacteria. However, gram-negative organisms grew less well in CLX bags. Their growth was either delayed, inhibited after a few days, or entirely suppressed. Our data suggest that (1) changing the storage period of platelets from 7 to 5 days is unlikely to reduce the incidence of clinical sepsis caused by gram-positive organisms if the number of organisms introduced at the time of contamination is on the order of 10 to 1000 bacteria; (2) gram-negative organisms tend to proliferate more slowly in CLX bags than in PL-732 bags; and (3) shortening the shelf life of platelets to 5 days may not eliminate gram-negative sepsis after transfusion of platelets stored in PL-732 bags, but it may reduce the number of such episodes associated with CLX bags.