Bacterial and fungal contamination risks in human oocyte and embryo cryopreservation: open versus closed vitrification systems

Objective To study the contamination risk in open and closed vitrification devices for oocyte/embryo cryopreservation by evaluating the contaminants present (bacteria and fungi) in the thaw medium and in liquid nitrogen (LN) storage containers. Design Retrospective study. Setting Human reproduction unit. Patient(s) None. Intervention(s) Retrospective study of vitrification device safety and LN sterility performed from July to October 2014. Main Outcome Measure(s) From each bank container, both open and closed vitrification devices, devitrification media and LN in the containers and as supplied by the company were evaluated for contaminants. An automated system and the corresponding susceptibility to antibiotics were used for bacteria identification. Fungus detection was performed by evaluating the colony morphology and their microscopic characteristics. Result(s) No bacteria or fungi were observed in any of the devitrification media regardless of the type of device used, nor in the LN supplied by the company. No fungi were observed in any of the LN samples tested. Stenotrophomonas maltophilia and Bacillus spp. were found in all oocyte/embryo bank LN containers. There was no relationship between the number of samples or the time that each container had been used and the presence of microbiologic contaminants in the LN. At the container's bottom, Acinetobacter lwoffii , Alcaligenes faecalis ssp. faecalis, and Sphingomonas paucimobilis were found. Conclusion(s) Bacteria cross-contamination may not occur in oocyte/embryo banking in either open or closed storage devices. However, microorganisms can survive in LN. The bacteria cross-contamination risk is no greater for open than for closed containers. Storage containers should be cleaned periodically owing to the risk of lost straws or small particles of contaminated material.