Male Fertility and the Semen Microbiome

It seems as if there is no limit to the various body systems that are now being characterized as having a unique association with bacteria and other resident living organisms. Several years ago, I wrote Brain Maker which explored the relationship of the gut related microbiome to general health and specifically, brain health. Quite recently, we have been exploring the oral microbiome in the context of its relationship to cardiovascular and neurodegenerative diseases.

Now, it appears that the semen microbiome might significantly affect a man’s health, particularly his fertility. The importance of these new findings cannot be overstated as over the past several decades, studies have shown a significant decline in male fertility among American men. Sperm counts, for example, show an average decrease of about 1.6% per year. A comprehensive meta-analysis reported a 52% decline in sperm concentration and a 59% decline in total sperm count in men from North America, Europe, Australia, and New Zealand from 1973 to 2011. Lifestyle-related health issues, which can impact fertility, such as obesity, have also been on the rise, with the prevalence of obesity in American men nearly tripling from 8% in the 1960s to over 30% in recent years. But how might these lifestyle factors ultimately affect fertility?

The link could be found in how lifestyle choices interact with the body’s native bacteria, specifically those found in semen.

Research conducted by the UCLA Department of Urology suggests that the microorganisms in semen may well affect sperm quality and male reproductive success. This interest stems from broader studies on the microbiome’s impact on human health, prompting an investigation into how semen’s microbial community might contribute to male infertility.

The research identifies a specific bacterium, Lactobacillus iners, linked to reduced fertility due to its potential to hinder sperm movement. This bacterium is known for producing L-lactic acid which could lead to inflammation affecting sperm. Although previously studied in the context of female reproductive health, this is the first study to explore its negative effects on male fertility.

And beyond this one bacterial strain, the study examines the presence of different strains of Pseudomonas bacteria in individuals with varying degrees of sperm health. It notes varied effects on fertility among closely related bacterial types, suggesting that similar microbes can have diverse impacts on reproductive outcomes.

Vadim Osadchiy, a UCLA Urology Department resident and study lead, emphasizes the preliminary nature of these findings but acknowledges their importance in guiding future research. He suggests that these results contribute to a growing body of evidence and will help direct further detailed studies to clarify the semen microbiome’s role in male fertility.