Male infertility has been on the rise, but its causes remain unclear despite advances in research. Nearly one-third of cases show abnormal semen analysis (SA) results, with the exact cause often undetermined. Recent studies suggest the microbiome, the collection of microorganisms in the body, may play a role in human health and disease, including male infertility. However, research specifically on the semen microbiome is still limited, and even fewer studies have connected it to fertility issues.
Previous research has found notable differences in the semen microbiome of infertile males compared to healthy individuals. One study found an association between the genus Pseudomonas and total motile sperm count. Another found that men with non-obstructive azoospermia (a condition where sperm is absent from the semen) had different microbiome diversity compared to healthy men.
Study Overview
The current study, conducted between August 2021 and June 2022, aimed to investigate the relationship between the semen microbiome and changes in SA parameters, such as sperm motility and concentration. Participants were adult males (18 years and older) who were either seeking fertility evaluation or had biological paternity before a vasectomy.
Key data points like age, circumcision status, body mass index (BMI), alcohol use, and smoking habits were collected. Semen samples were provided after a period of abstinence, and they were analyzed before any fertility treatments. Semen quality was assessed using an automated analyzer, with high-powered microscopy used for those with azoospermia or oligozoospermia (low sperm count).
The researchers used DNA extraction and sequencing to examine the semen microbiome, focusing on 16S ribosomal RNA to identify bacterial species present. They also assessed the diversity of bacterial communities using several bioinformatics methods, including principal coordinate analysis (PCoA).
Participants were divided into three groups based on SA results: 1) those with normal sperm motility and concentration, 2) those with normal motility, and 3) those with normal sperm concentration. Comparisons were made between the groups to examine any differences in the semen microbiome.
Key Findings
The study included 73 males with an average age of 37.94 years and an average BMI of 26.73. About 78% were circumcised. No significant differences in age, BMI, circumcision status, alcohol use, or smoking habits were found between the groups.
Microbiome diversity, both alpha (species richness) and beta (community composition), was similar across the three groups. The five most abundant species found across all participants were Corynebacterium tuberculostearicum, Enterococcus faecalis, Finegoldia magna, Lactobacillus iners, and Staphylococcus epidermidis.
However, there were some differences in bacterial abundance between those with normal and abnormal SA parameters. For example, participants with normal semen analysis had a higher abundance of S. hominis and a lower abundance of Peptoniphilus coxii compared to those with abnormal results. Men with normal sperm motility had less L. iners than those with abnormal motility, while Pseudomonas stutzeri and Pseudomonas fluorescens were less abundant in those with abnormal sperm concentration.
Age, semen volume, sperm motility, and concentration were all significantly associated with variations in bacterial composition.
Conclusion
The study suggests that certain microbes may influence sperm parameters. Specifically, L. iners was found to be more abundant in men with abnormal sperm motility, which supports earlier studies indicating that this species could negatively impact fertility. While the study does not prove causality, it highlights that a small subset of microbes could be important in male fertility. Future research could further explore the role of the semen microbiome in fertility, offering potential new avenues for treatment.
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