Evaluation of pooled cultures for bacterial detection in whole blood-derived platelets

The BacT/ALERT (bioMérieux) system is highly efficient for bacterial detection in apheresis platelets (PLTs) and whole blood-derived PLTs produced by the buffy-coat method. Detection of bacterial contamination in whole blood-derived PLTs produced by the PLT-rich plasma (PRP) method, however, is problematic. Prestorage pooling of these PLTs is not permitted in some countries including Canada and the United States, and culturing individual units is costly and may significantly reduce the PLT unit content. In this study, the sensitivity and specificity of BacT/ALERT cultures performed on pools derived from PRP PLTs are reported.

The sensitivity of the BacT/ALERT system was evaluated for bacterial detection in PRP PLTs with a dilution effect. Thirty PLT pools were produced with 1 PLT unit previously spiked with bacteria and then pooled with other four nonspiked PLT units. Three bacteria, usually associated with PLT contamination, were selected for spiking. The specificity of this method was evaluated in 40 nonspiked PLT pools.

The method was found to be 100 percent specific and 97 percent sensitive. Of the five spiked pools with Streptococcus pneumoniae at levels of less than 2 colony-forming units (CFUs) per mL, four were found to be positive whereas all 25 spiked pools with greater than 9 CFUs per mL of any of the chosen bacteria gave positive results. The mean time of detection was 17 to 19 hours for Staphylococcus epidermidis and 14 to 15 hours for S. pneumoniae and Pseudomonas aeruginosa when spiked with similar bacterial inocula.

The evaluated system is highly sensitive and specific and may be a feasible method for bacterial detection in PRP PLTs.