Semen microbiome linked to human infertility

Microbiomes – the microbes that live alongside us – have been implicated in cancer, healthy brains, and even personality, but a new study has found the specific microbiome of semen may impact male fertility.

“The [cause] of abnormal semen analysis parameters is not identified in 30% of cases; investigations involving the semen microbiome may bridge this gap,” researchers from the University of California and the University of Texas write in Scientific Reports.

Inside semen are several sperm helpers like enzymes, fructose and citric acid. There are also plenty of bacteria, such as Lactobacillus, Enterococcus, Corynebacterium and Staphylococcus.

The researchers hypothesised that differences in the quantity or type of bacteria might affect fertility, and recruited 73 men who were either undergoing a vasectomy consultation or fertility evaluation.

These groups are a good start for comparing differences in semen microbiomes, as one group was struggling to have kids, while another had successfully had children.

They looked at sperm motility and sperm concentration, and split them into groups based on this.

The 5 most common species – Enterococcus faecalisCorynebacterium tuberculostearicumLactobacillus inersStaphylococcus epidermidis, and Finegoldia magna – were found in both groups.

But there were some differences.

Those with abnormal sperm concentration had more Pseudomonas stutzeri and Pseudomonas fluorescens but fewer Pseudomonas putida. Those with abnormal sperm motility had a higher abundance of L. iners.

L. iners is particularly interesting. Other research has looked at this particular bacterium in fertility, but only in the vaginal microbiome.

“In a study that included 25 couples undergoing the use of assisted reproductive technologies, researchers found that increased abundance of vaginal lavage [fluid] Lactobacillus iners was associated with infertility,” the researchers wrote.

“Our study represents the first report of a negative association between Lactobacillus iners and male-factor fertility.”

It’s worth noting the differences between groups are small and a change in just one microbe may have complex causes.

“There is much more to explore regarding the microbiome and its connection to male infertility,” said the study’s lead author Vadim Osadchiy, a resident urologist at the University of California Los Angeles.

“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.”   

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