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Semen Microbiome Could Be Linked to Male Infertility

A man carrying his child.
Credit: Kelli McClintock / Unsplash.
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There has been a surge in microbiome research over recent years. A growing number of studies are establishing correlations or direct links between our microbial composition and state of health. Now, a new study has established a link between semen microbiota and sperm parameters.

The research, published in Scientific Reports, was led by Dr. Vadim Osadchiy, physician and resident in the Department of Urology at the University of California Los Angeles (UCLA).

What causes male factor infertility?

An estimated one in seven couples are infertile, and in up to 50% of these cases, male factor infertility is the major contributor. Despite its high prevalence, the causes of male factor infertility are only partially understood.

What can cause male factor infertility?

Male factor infertility might be caused by issues including, but not limited to, the production of abnormal sperm, low sperm production or blockage of sperm delivery.

Techniques such as next-generation sequencing can sequence the microbes present in a sample, such as sperm. While a number of studies have explored the semen microbiome in relation to fertility, they have largely been retrospective and limited by small sample sizes.

Osadichy and colleagues obtained semen samples from a total of 73 men with an average age of 38. Participants had presented for either an infertility evaluation, or for a consultation for a vasectomy having already parented a child. They were stratified into three groups based on semen analysis (SA) parameters:

  • Group one – normal sperm concentration and motility, vs at least one abnormality in sperm concentration or mobility
  • Group two – normal vs abnormal sperm motility
  • Group three – normal vs abnormal sperm concentration.

Lactobacillus iners associated with abnormal sperm parameters

“Aligned with previous studies, our results reveal that semen harbors a diverse, but largely consistent, microbiome. The most abundant members of this niche were Enterococcus faecalis, Staphylococcus epidermidis, Corynebacterium tuberculostearicum and Lactobacillus iners,” the researchers explained.

When the researchers considered semen volume, concentration and motility, L. iners transpired to be the bacterium most associated with abnormal sperm parameters. This species has been linked to fertility in previous studies, though largely in relation to the vaginal microbiome and female fertility. “Our study represents the first report of a negative association between Lactobacillus iners and male factor fertility,” the authors said.

“There is much more to explore regarding the microbiome and its connection to male infertility,” Osadchiy said. “However, these findings provide valuable insights that can lead us in the right direction for a deeper understanding of this correlation. Our research aligns with evidence from smaller studies and will pave the way for future, more comprehensive investigations to unravel the complex relationship between the semen microbiome and fertility.”  

Reference: Osadchiy V, Belarmino A, Kianian R, et al. Semen microbiota are dramatically altered in men with abnormal sperm parameters. Sci Rep. 2024;14(1):1068. doi: 10.1038/s41598-024-51686-4

This article is a rework of a press release issued by the University of California Los Angeles.