A reliable procedure for decontamination before thawing of human specimens cryostored in liquid nitrogen: three washes with sterile liquid nitrogen (SLN2)

ObjectiveTo report a washing procedure, to be performed as frozen specimens are taken out of cryobanks, to minimize the risk of hypothetical culture contamination during thawing.DesignBasic research.SettingPrivate assisted reproduction center.Intervention(s)Two batches of liquid nitrogen (LN2) were experimentally contaminated, one with bacteria (Pseudomonas aeruginosa, Escherichia coli, Stenotrophomonas maltophilia) and the other with fungi (Aspergillus niger). Two hundred thirty-two of the most common human gamete/embryo vitrification carriers (Cryotop, Cryoleaf, Cryopette) were immersed in the contaminated LN2 (117 in the bacteria and 25 in the fungi-contaminated LN2). The carriers were tested microbiologically, one group without washing (control) and the other after three subsequent washings in certified ultraviolet sterile liquid nitrogen (SLN2). The carriers were randomly allocated to the “three-wash procedure” (three-wash group, 142 carriers) or “no-wash” (control group, 90 carriers) using a specific software tool.Mean Outcome Measure(s)Assessment of microorganism growth.Result(s)In the no-wash control group, 78.6% of the carriers were contaminated by the bacteria and 100% by the fungi. No carriers were found to be contaminated, either by bacteria or fungi, after the three-wash procedure.Conclusion(s)The three-wash procedure with SLN2 produced an efficient decontamination of carriers in extreme experimental conditions. For this reason, this procedure could be routinely performed in IVF laboratories for safe thawing of human specimens that are cryostored in nonhermetical cryocontainers, particularly in the case of open or single-straw closed vitrification systems.