Metagenomics Reveals Specific Microbial Features in Males with Semen Alterations

Abstract

Infertility incidence is rising worldwide, with male infertility accounting for about 50% of cases. To date, several factors have been associated with male infertility; in particular, it has been suggested that semen microbiota may play a role. Here, we report the NGS-based analyses of 20 semen samples collected from men with (Case) and without (Control) semen alterations. Genomic DNA was extracted from each collected sample, and a specific PCR was carried out to amplify the V4-V6 regions of the 16S rRNA. Sequence reactions were carried out on the MiSeq and analyzed by specific bioinformatic tools. We found a reduced richness and evenness in the Case versus the Control group. Moreover, specific genera, the Mannheimia, the Escherichia_Shigella, and the Varibaculum, were significantly increased in the Case compared to the Control group. Finally, we highlighted a correlation between the microbial profile and semen hyperviscosity. Even if further studies are required on larger groups of subjects to confirm these findings and explore mechanistic hypotheses, our results confirm the correlation between semen features and seminal microbiota. These data, in turn, may open the way to the possible use of semen microbiota as an attractive target for developing novel strategies for infertility management.

Characterisation and comparison of semen microbiota and bacterial load in men with infertility, recurrent miscarriage, or proven fertility

“…We did not observe any significant associations between bacterial clusters, richness, diversity or load with traditional seminal parameters, sperm DNA fragmentation or semen ROS. This is in contrast with Veneruso et al, who reported that in infertile patients, semen bacterial diversity and richness was decreased whereas Lundy et al, reported that diversity was increased in infertile patients (9, 31). Further, Lundy et al, reported Prevotella abundance to be inversely associated with sperm concentration; this was not replicated in our study (9).…”

“…Recent studies have characterised the semen microbiota in health men and those with infertility(5, 6, 8, 9, 10, 11, 31). We have extended these findings by analysing a larger sample of men subclassified into different reproductive disorders likely to arise from poor semen quality.…”

“…We have extended these findings by analysing a larger sample of men subclassified into different reproductive disorders likely to arise from poor semen quality. Unlike most prior studies, we were able to phenotype men with molecular markers of reproductive function such as seminal ROS and sperm DNA fragmentation, which are known to damage sperm (5, 6, 8, 9, 10, 11, 31). classical seminal parameters, but also key functional parameters.…”

“…classical seminal parameters, but also key functional parameters. Furthermore, we incorporated stringent negative controls to permit removal of sequences likely originating from extraction kits and reagents known to contaminant low biomass samples such as semen (6, 8, 31). This is important since Molena et al report that 50%-70% of detected bacterial reads may be contaminants in a sample from testicular spermatozoa (32); with the addition of accessory gland secretions and passage along the urethra it is likely that contamination of ejaculated semen would be much higher.…”

“…Several previous studies have described semen microbiota composition to genera level and some have reported associations between specific genera and parameters of semen quality and function (5, 6, 8, 9, 10, 11, 31). However, in many cases these studies have failed to consider multiple comparisons testing, likely leading the reporting of spurious associations.…”