Growth of bacteria in inoculated platelets: implications for bacteria detection and the extension of platelet storage

BACKGROUND: Recent reports from Europe have advocated the use of bacterial culturing of platelets an Day 2 or 3 of storage to extend the shelf life of platelets to 7 days, thereby reducing the outdating of platelets and prese rving a limited medical resource. To assess the optimal timing, the necessa ry sensitivity, and the possible efficacy of bacterial detection, the bacte rial growth characteristics were reviewed in 165 platelet units, each inocu lated on the day of collection with one of the following organisms: Bacillu s cereus, Pseudomonas aeruginosa; Klebsiella pneumoniae, Serratia marcescen s, Staphylococcus aureus, and Staphylococcus epidermidis from four previous ly published studies. STUDY DESIGN AND METHODS: Quantitative culture data from inoculated platele t concentrates from five sites and four studies were combined into one data base and analyzed for bacterial concentration thresholds (greater than or e qual to 10(1), greater than or equal to 10(2), greater than or equal to 10( 3), greater than or equal to 10(4), greater than or equal to 10(5) CFU/mL) by day of storage. RESULTS: All examples of B. cereus, P. aeruginosa, K. pneumoniae, S. marces cens, and S. aureus had concentrations greater than or equal to 10(2) CFU p er mL by Day 3 after inoculation. By Day 4, all units with these organisms contained greater than or equal to 10(5) CFU per mL. Units contaminated wit h S. epidermidis showed slower and more varied growth. By Day 3 after inocu lation. 81.3 percent had 10(2) CFU per mL. By Day 4 after inoculation, 46 ( 95.8%) of 48 units had concentrations greater than or equal to 10(2) CFU pe r mL. CONCLUSION: These experiments suggest that an assay capable of detecting 10 (2) CFU per mL on Day 3 of storage would detect the vast majority of bacter ially contaminated platelet units, prevent many cases of platelet-associate d bacterial sepsis, and provide a scientific basis for the extension of the current platelet storage time. It would be expected that a rare, slow-grow ing organism could escape such a detection scheme.