Evaluation of the BacT/Alert automated blood culture system for detecting bacteria and measuring their growth kinetics in leucodepleted and non-leucodepleted platelet concentrates

Background and Objective To evaluate the BacT/Alert automated blood culture system for the detection of bacteria in platelet concentrates, and to determine bacterial growth kinetics in leucodepleted and non-leucodepleted units. Materials and Methods Apheresis (Cobe Leucocyte Reduction System(TM) [LRS]) and pooled buffy coat-derived (Optipress(TM)) platelet concentrates (PCs) were tested. Six organisms were used for spiking the PCs: Clostridium perfringens, Bacillus cereus, Group B Streptococcus, Staphylococcus epidermidis, Staphylococcus aureus and Escherichia coli. Units were inoculated to give a final concentration of approximate to 1 and 50 colony-forming units (CFU)/ml. On days 0, 2 and 5, BacT/Alert standard aerobic and anaerobic bottles were inoculated with a 5-ml fill volume and bacteria were enumerated. Results The BacT/Alert Automated blood culture system gave rapid determination times of spiked units, with all positives detected within 48 h and 98.1% detected within 24 h. In general, as the inoculum concentration increased, the detection time decreased. Rapid growth was obtained with all organisms tested except for B. cereus, which failed to grow on four occasions. Bacterial numbers on day 2 ranged from 10(5) to 10(11) CFU/ml and on day 5 ranged from 10(4) to 10(12) CFU/mL Growth was not significantly greater in leucodepleted units. Conclusions The study confirmed that PCs are an excellent growth medium for bacteria. Rapid and substantial growth was obtained with all organisms under test. Leucodepletion does not appear to enhance bacterial proliferation. The BacT/Alert automated blood culture, system could rapidly detect contamination of units. Bacterial screening using an automated blood culture system is therefore a potential option.