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.
In addition, the researchers discovered that three types of bacteria from the Pseudomonas group – a very common type of bacteria – were found in patients with both normal and abnormal sperm concentrations.
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.
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.
‘There is much more to explore regarding the microbiome and its connection to male infertility,’ said lead author Dr Vadim Osadchiy.
‘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.’
Globally, fertility rates are falling, with poor diet and lifestyles also thought to play a role in men’s health.