Microbial screening of unrelated cord blood units in a Chinese cord blood bank

Abstract

Background: Given limited sample volume available for sterility testing, optimal testing methods and algorithms of cord blood (CB) have not been established according to standards.

Study design and methods: The volume of CB unit was reduced to 20 mL in a closed system. Hetastarch and cryopreservation solution was added to the processed CB unit in Class 100 environment. In the routine sterility testing, 20 mL of red blood cells (RBC) sample was cultured in aerobic and anaerobic culture bottles. In verification post-thaw culture of the final product, some of the discarded final product units were also sampled and cultured after thaw. All the culture bottles were incubated in the BacT/ALERT 3D system.

Results: In the routine sterility testing, 139 of 7032 CB units (1·98%) were contaminated with microorganism. In 84 of these 139 units (60·4%) only the anaerobic bottle was positive. Lactobacillus spp. were the most prevalent contaminant. Sixty-two discarded CB stem cell units were recultured after thaw. Of these, 10 of 48 units with a positive culturing of RBC sample were negative in the post-thaw reculture. One of 14 units with negative culturing of RBC sample was contaminated with Bifidobacterium breve in special verification test.

Conclusion: Our study demonstrates the predominant organisms implicated in CB microbial contamination were part of the human intestinal and vaginal flora. The larger sample volume and anaerobic culture would significantly increase the detection rate of microbial contaminated CB. We also found that potential transfusion-transmitted bacterial infection risk still existed in final product although microbial screening was performed.

Keywords: BacT/ALERT; cord blood; sterility testing.