Sterility testing of apheresis hematopoietic progenitor cell products using an automated blood culture system

AABB Standards require monitoring of hematopoietic progenitor cell (HPC) products for microbial contamination. To date, there is no automated blood culture system cleared by the Food and Drug Administration for this application. Our objective was to validate the VersaTREK system (TREK Diagnostic Systems) for sterility testing of apheresis HPC products.

Four aerobic bacteria (Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus mitis, and Bacillus cereus), five anaerobic bacteria (Fusobacterium necrophorum, Clostridium perfringens, Bacteroides fragilis, Prevotella loescheii, and Propionibacterium acnes), and one fungus (Candida albicans) were spiked into apheresis HPC products at concentrations of 10, 10(2) , 10(3) , and 10(4) colony-forming units (CFUs)/mL. Aerobic and anaerobic bottles were incubated until positive or for up to 5 days. DNA was simultaneously extracted for polymerase chain reaction amplification of 16S ribosomal RNA (rRNA) gene.

All aerobic bacteria grew in both bottles at all concentrations tested within 24 hours, and the time to positivity (TTP) was significantly shorter with aerobic bottles. C. albicans grew in the aerobic media at all concentrations within 30 hours. Anaerobes grew in the anaerobic bottle at all concentrations within 5 days. No bacteria were detected by using 16S rRNA gene amplification at 10(4)  CFUs/mL.

Compared to culture, 16S rRNA gene amplification of HPCs does not improve sensitivity or turnaround time for HPC sterility testing. The VersaTREK system is a reliable tool for detecting microbial contamination of apheresis HPC products with a limit of detection of less than or equal to 10 CFUs/mL. Inclusion of both the aerobic and the anaerobic culture bottles achieves the shortest TTP for all species tested.