Men are becoming less fertile – scientists may have just found a reason why

Sperm cells, illustration — Bacteria could be causing trouble for sperm (Picture: Getty/Science Photo Libra)

You’ve heard of the gut microbiome, and probably skin microbiome, but did you know there’s also a semen microbiome – and that it could affect fertility?

That is the finding of a new study by the department of urology at the University of California, Los Angeles (UCLA).

Microbiome refers to the collection of microbes – bacteria, fungi and viruses – that affect human health. While there have been many studies into the microbiomes found in the digestive system and on the skin, there has been less focus on the reproductive systems, particularly in men.

However, the UCLA team found that one microbe in particular, the bacteria Lactobacillus iners, can have a direct negative impact on sperm motility, which in turn affects fertility.

The microbe is more widely known as the cause of bacterial vaginosis in women, and is the most commonly found bacteria found in the female genital microbiome.

While the study, published in Scientific Reports, was not able to pinpoint the exact link, previous research has revealed Lactobacillus iners can produce L-lactic acid (the less common of the two types of lactic acid), which can lead to localized inflammation. This inflammation may impact sperm motility.

Bacteria, illustration — Our bodies are full of bacteria, inside and out (Picture: Getty/Science Photo Libra)

Microbes called Pseudomonas fluorescens and Pseudomonas stutzeri were more common in patients with abnormal sperm concentrations, while Pseudomonas putida was less common in samples with abnormal sperm concentrations.

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The finding highlights how even closely-related microbes can have a different effect on human health, and that not all bacteria found in semen will have an impact on fertility.