Sterilization of liquid nitrogen with ultraviolet irradiation for safe vitrification of human oocytes or embryos

Objective: To evaluate the efficacy of ultraviolet (UV) irradiation for rapid microbial decontamination of liquid nitrogen (LN2). Design: Basic research. Setting: Private assisted reproduction center. Animal(s): Microorganisms (bacteria and fungi). Intervention(s): Two stainless steel open dewars containing LN2 were contaminated in a two-step experiment with high titers of cultures of bacteria (Stenotrophomonas maltophilia, Pseudomonas aeruginosa, and Escherichia coli) and fungi (Aspergillus niger). One of the two dewars was subsequently exposed to UV irradiation at 253.7 nm to obtain a rapid microbial decontamination before the complete evaporation of LN2. Main Outcome Measure(s): Detection of the micro-organisms in LN2 after UV sterilization through the assessment of bacterial and fungal growth in minimal and selective Petri dishes. Result(s): None of the contaminating micro-organisms were detected in LN2 after UV sterilization. Conclusion(s): Decontamination of LN2 with UVirradiation is feasible and straightforward. The fact that LN2 can be quickly and safely sterilized should encourage the wider application of human oocyte and embryo vitrification with open carriers. (Fertil Steril (R) 2010;94:1525-8. (C) 2010 by American Society for Reproductive Medicine.)