Men's Testes Have a 'Microbiome.' Could It Affect Fertility?

A man in consultation with a doctor.
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Men's testes were once thought to be free of bacteria, but a small new study from Italy suggests that microorganisms may live naturally in this part of the male reproductive system.

What's more, the findings suggest that this so-called testicular microbiome may be different in men with a type of infertility called azoospermia, who have no measurable sperm in their semen, than it is in fertile men.

Still, the findings are very preliminary, and much more research is needed to confirm if the testicular microbiome actually affects sperm production, the researchers said. But if the findings hold up, studies on the testicular microbiome might one day lead to the development of new therapies for men with azoospermia, who currently have few treatment options, experts say. [Trying to Conceive: 12 Tips for Men]

"These findings are actually surprising, because almost all medical textbooks mention that [the] human testes … is a microbiologically sterile microenvironment," said study lead author Massimo Alfano, a senior scientist at the Urological Research Institute at the IRCCS Hospital San Raffaele in Milan. But with new technologies, "for the first time ever, we [have] been able to quantify the bacterial DNA" in the testes, Alfano told Live Science.

"If confirmed and expanded, these results could support future … therapies for male factor infertility" such as those based on restoring a proper "testicular niche," Alfano said.

The study was published May 30 in the journal Human Reproduction.

Testicular microbiome

About 1 percent of all men, and 10 to 15 percent of men with infertility, have azoospermia, according to the Cleveland Clinic. Couples in which the man has azoospermia cannot become pregnant naturally, because there is no sperm in the man's ejaculate, said Dr. Sarah Vij, a urologist at the Cleveland Clinic who was not involved with the study.

"Those are the men that we really want to be able to help the most," Vij said, referring to men with azoospermia. "Some of those men [with azoospermia] have no options to have a biological child."

The most severe form of azoospermia is "non-obstructive azoospermia," which means the condition results from poor sperm production, rather than a blockage that prevents sperm from getting into the semen. The only treatment option for non-obstructive azoospermia is a surgery that attempts to retrieve sperm from the testicular tissue, which is not always successful, Vij told Live Science.

For the new study, the researchers analyzed testicular tissue from 10 men with non-obstructive azoospermia, as well as testicular tissue from five men without azoospermia who produced normal amounts of sperm. Among the men with azoospermia, half had successful surgeries that retrieved sperm, while half had unsuccessful surgeries that didn't retrieve any sperm.

The researchers found that the men without azoospermia had small amounts of bacteria in their testes, and these bacteria belonged to four main groups, called Actinobacteria, Bacteroidetes, Firmicutes and Proteobacteria.

The men with azoospermia had more bacteria overall in their testes, but their testicular microbiome was less diverse: The researchers found only two groups of bacteria — Actinobacteria and Firmicutes — in these men. What's more, the men who didn't have sperm retrieved during surgery had even less diversity in their microbiome, which was dominated mainly by Actinobacteria.

Avoiding surgery?

"I definitely applaud what they've done," Vij said of the study. "I think it has potential significance."

Currently, doctors do not have a way to predict which men with azoospermia will have successful sperm retrieval from surgery, Vij said. But the new findings raise the question of whether the testicular microbiome might help predict successful sperm retrieval. "If the microbiome can enable us to predict who is going to have success, we could probably spare some men surgery," she said.

In addition, if the findings are confirmed, it's possible that the testicular microbiome "could help guide future therapies for men, to give them another option" besides surgery, Vij said.

Still, even if future studies confirm the results, there are many more steps needed before the findings could be meaningful for patients. For example, the current study used testicular biopsies to describe the microbiome, but these procedures are invasive. "We have to figure out a way to assess the microbiome noninvasively, to have meaning" for patients, Vij said.

Additional studies would also need to examine whether changing the microbiome could have an effect on sperm production, she said.

In 2016, early research also suggested that women's fallopian tubes and ovaries may have microbiomes.

Original article on Live Science.

Rachael Rettner

Rachael is a Live Science contributor, and was a former channel editor and senior writer for Live Science between 2010 and 2022. She has a master's degree in journalism from New York University's Science, Health and Environmental Reporting Program. She also holds a B.S. in molecular biology and an M.S. in biology from the University of California, San Diego. Her work has appeared in Scienceline, The Washington Post and Scientific American.