Evaluation of the inhibitory effects of vaginal microorganisms on sperm motility in vitro

Female infertility usually occurs as a result of ageing, physical impairment, hormone disturbances and lifestyle or environmental factors. However, the potential role of Lactobacillus in female infertility has remained largely unexplored. In the present study, high-throughput sequencing, real-time PCR, bacterial adherence assays and sperm motility assays were used to evaluate the microbial diversity, adherence properties and effect on sperm motility of sperm bacteria, vaginal bacteria and vaginal bacteria that had been co-cultured with sperm. The results indicated that in the co-culture group, Lactobacillus adhered to sperm cells in numbers that were 332-fold higher than those of control species Enterococcus and analysis of sequencing data using the Kyoto Encyclopedia of Genes and Genomes indicated that adhered microbes reduced sperm cell motility. Vaginal isolates, as well as bacterial strains used as controls, were co-cultured with sperm and it was indicated that all strains were able to adhere to sperm cells in large numbers. The probiotic Lactobacillus (L.) strains L. crispatus, L. acidophilus, L. helveticus and L. gasseri significantly reduced sperm motility (based on measurements of general, straightforward and non-straightforward progressive motility, total motility and average path velocity; P<0.05). Furthermore, L. crispatus, L. acidophilus, L. salivarius, L. helveticus and L. gasseri markedly reduced sperm penetration in a viscous medium. Based on these results, it may be hypothesized that the weakening effect of Lactobacillus on sperm motility may be beneficial for healthy couples to prevent the combination of abnormal sperms and eggs, but may be detrimental for males with severe asthenospermia, oligospermia or aspermia.