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Published on: January 29, 2021
Liquid nitrogen freezers: a potential source of microbial contamination of hematopoietic stem cell components
D Fountain1, M Ralston, N Higgins
1Brigham and Women's Hospital, Beth Israel Deaconess Medical Centèr, Boston, Massachusetts, USA.
Background:
The recent report of hepatitis B transmission between hematopoietic progenitor and putative stem cell (HPC) components stored in liquid nitrogen led to the questioning of whether evidence existed for similar contamination by bacterial or fungal elements.
Study Design And Methods:
Microbial contamination rates were reviewed for 704 HPC components from 255 patients over an 18-month period. Five liquid nitrogen freezers were surveyed for microbial contamination. The literature was reviewed to ascertain the published experience of other laboratories with HPC component contamination first documented on thawing.
Results:
Seven (1.2%) of 583 thawed components were found to be contaminated with a variety of environmental or waterborne organisms, despite a meticulous protocol to prevent contamination during thawing. All of these components had been sterile on cryopreservation. Literature review revealed a similar incidence of post-thaw contamination from other centers. Microbial survey of liquid nitrogen freezers revealed low-level contamination in four of five. The organisms represented were similar to those cultured from thawed HPC components. One freezer was heavily contaminated by Aspergillus species.
Conclusion:
Liquid nitrogen freezers are not sterile, and both the liquid and vapor phases are potential sources of microbial contamination of HPC components. While low-level contamination by environmental organisms may be common, the occurrence of heavy contamination by potential pathogens such as Aspergillus species suggests that monitoring of liquid nitrogen sterility may be indicated. Strategies to assess and prevent microbial transmission from liquid nitrogen to HPC components need further development.
Insights
Liquid nitrogen freezers can contaminate hematopoietic progenitor cell (HPC) components with bacteria and fungi. Monitoring freezer sterility is crucial to prevent microbial transmission and ensure patient safety.
Area of Science:
- Stem Cell Biology
- Microbiology
- Transplantation Immunology
Background:
- Hepatitis B transmission via hematopoietic progenitor cell (HPC) components highlights risks.
- Potential for bacterial or fungal contamination in cryopreserved HPCs is a concern.
Purpose of the Study:
- To investigate microbial contamination rates in HPC components stored in liquid nitrogen.
- To assess the sterility of liquid nitrogen freezers used for HPC storage.
Main Methods:
- Reviewed microbial contamination in 704 HPC components over 18 months.
- Surveyed five liquid nitrogen freezers for microbial contamination.
- Conducted a literature review on post-thaw HPC contamination.
Main Results:
- 1.2% of thawed HPC components showed microbial contamination, despite sterile cryopreservation.
- Liquid nitrogen freezers exhibited low-level contamination; one had significant Aspergillus species.
- Contaminating organisms were environmental or waterborne, matching those in thawed HPCs.
Conclusions:
- Liquid nitrogen freezers are a potential source of HPC microbial contamination.
- Monitoring liquid nitrogen sterility is recommended, especially due to pathogens like Aspergillus.
- Developing strategies to prevent microbial transmission to HPCs is necessary.
