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

The dominant species of vaginal bacteria, Lactobacilli, have important roles in maintaining female reproductive fitness. However, no studies have been carried out to evaluate their potential negative effects on sperm motility. In the present study, we analysed the microbial diversity, adherence properties and effect of sperm motility of sperm bacteria (SM), vaginal bacteria (VM) and vaginal bacteria that had been co-cultured with sperm (AM). These analyses were carried out using high-throughput sequencing, real-time PCR, adherence assays and sperm motility assays. Our results indicated that in the AM group, Lactobacilli adhered to sperm cells in numbers that were 332-fold higher than seen for Enterococcus (used as a control species). As the KEGG PATHWAY data indicated that adhered microbes may reduce cell motility, we co-cultured the vaginal isolates – as well as some in-house bacterial strains for use as controls – with sperm and found that all strains, both probiotic and pathogenic, adhered to sperm cells in large numbers. The probiotic strains Lactobacillus crispatus, L. acidophilus, L. helveticus and L. gasseri caused significantly decreased sperm motility (based on measurement of PRA, PRB, PR, total motility and average path velocity) (p < 0.05). Moreover, L. crispatus, L. acidophilus, L. salivarius, L. helveticus and L. gasseri caused greatly reduced sperm penetration of a viscous medium. We discovered that Lactobacilli adhesion causes a significant decrease in sperm motility. It is our hypothesis that the reduction in motility may be beneficial for healthy couples to prevent the combination of abnormal sperms and eggs but could be severely detrimental for men with severe asthenospermia, oligospermia or aspermia.