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A recently identified bacteria in semen could affect sperm motility and cause fertility problems, a study by American researchers shows.

The authors of the study recall that around half of the infertility situations within a couple can be traced back to the man. “The problem is that we don't really know what the causes of the problem are in humans,” commented Professor Bernard Robaire, who teaches in the Department of Obstetrics and Gynecology at McGill University. Half or two-thirds of cases are idiopathic and we don't really know what the cause is.” Only recently have scientists discovered that sperm are not a sterile environment and have their own microbiome. However, a comprehensive inventory of this microbial flora has never been conducted.

Researchers at the University of California at Los Angeles took on this task and examined the sperm of 73 men; Half of them were already fathers, and the other half had seen a doctor because of fertility problems. The study authors identified five bacteria present in both groups, but high levels of the bacterium Lactobacillus iners were associated with motility problems (the ability of sperm to “swim” effectively) in the infertile group. Even more interestingly, the researchers point out that the same bacteria is also present in the vaginal microbiome and that high levels may also be linked to fertility problems in women.

This study is only the very first to address this issue, and so researchers are still a long way from understanding how the L. iners bacterium affects sperm motility. One hypothesis is that inflammation is caused by the bacteria. However, other studies have found a link between other members of the Lactobacillus family and motility problems – which could mean that the bacteria actually play a useful role in containing less vigorous sperm so that the healthiest ones can join the egg.

“The question we need to ask is: Are these bacteria present in the reproductive system or are they associated with other tissues? » asked Professor Robaire. It is not yet clear where and how these bacteria enter the reproductive system.” Still, he continues, identifying this bacterium in the semen of men with fertility problems could potentially lead to new diagnostic tests or even treatments, even if not for tomorrow be the case.

Unfortunately, the effectiveness of in vitro fertilization has led to less research being done into the causes of male infertility, recalls Professor Robaire. And even if the problem is on the man's side, it is often the woman who suffers the consequences of the treatment, “that's why it is very important to try to understand the cause of infertility in men.” “In-vitro Fertilization is a simple solution,” said Professor Robaire. However, for patients it is an expensive solution from which fertilization clinics benefit financially.

The results of this study were published in the journal Scientific Reports.

Photo credit: AP Photo/Wong Maye-E.