Evaluation of the sterility testing process of hematopoietic stem cells at Canadian Blood Services

BACKGROUND: Sterility testing of hematopoietic stem cells (HSCs) at The Canadian Blood Services Stem Cell Laboratory is performed using BacT/ALERT aerobic (SA) culture bottles. This study was conducted to verify the efficacy of this method and to assess the use of the BacT/ALERT aerobic (BPA) and anaerobic (BPN) culture bottles for microbial testing of HSCs. STUDY DESIGN AND METHODS: HSC products, including cryopreserved apheresis peripheral blood, marrow, and cord blood and fresh cord blood, were spiked with four aerobic organisms including Staphylococcus epidermidis, Bacillus cereus, Pseudomonas aeruginosa, and Candida albicans, and the anaerobe Bacteroides fragilis at a target concentration of 100 colony-forming units (CFUs)/mL. One to 2 mL of pre- and postspiked samples was inoculated into SA, BPA, and BPN bottles in duplicate and incubated for 5 to 10 days. The presence of the testing organisms in positive culture bottles was confirmed by plating on blood agar. RESULTS: The BacT/ALERT system detected the aerobic organisms in all HSCs in SA and BPA bottles within 34.1 hours while B. fragilis was detected only in BPN bottles within 68.6 hours. The mean recovered concentration of microorganisms in the HSC products ranged from 55 to 352 CFUs/mL with the exception of B. cereus, which was greater than 103 CFUs/mL. CONCLUSION: This study shows that the current sterility testing process at the Canadian Blood Services Stem Cell Laboratory detected the tested aerobic but not the anaerobic microbial contaminants in HSCs. The ability of the BacT/ALERT system using BPA and BPN bottles to detect bacterial contamination in HSCs was also demonstrated.