Around 3 million people in France are thought to be affected by infertility, 30% of whom are men. Worldwide, it affects one couple in six. A recent study suspects that sperm microbiota is a cause of male infertility.

Male infertility: definition, causes and key figures  


‘Infertility is a disorder of the male or female reproductive system defined as the inability to achieve pregnancy after 12 months or more of regular unprotected sexual intercourse’ (WHO*).


It is now estimated that 30% of infertility cases are male.


Male infertility can be caused by several factors, including:

  • Obstruction of the reproductive tract causing malfunction of seminal fluid excretion;
  • Hormonal disorders, particularly of testosterone, which regulates sperm production;
  • Inability of the testicles to produce spermatozoa, particularly because of certain drugs that alter sperm-producing cells;
  • Abnormal sperm function and quality (morphology, motility, etc.).


However, in a third of cases of male infertility, the causes remain unexplained.


Between 1973 and 2011, sperm counts in men in North America, Europe, Australia and New Zealand fell by 50 to 60%. This is why a sperm analysis, called a spermogram, is generally prescribed if there is any doubt about infertility.


A recent study incriminates sperm microbiota in male infertility

Sperm is far from sterile. It harbours a diverse microbiome, with bacteria such as Enterococcus faecalis, Staphylococcus epidermidis, Corynebacterium tuberculostearicum and Lactobacillus iners.


In a recent study published in the journal Scientific Reports, scientists analysed the composition of the sperm microbiota of 73 men. This microbial analysis was combined with a spermogram to examine the number, vitality, morphology and mobility of their spermatozoa.


On examination, the men with an abnormal sperm count had a different bacterial composition to the sperm microbiota of healthy men:

  • For those with an abnormally low sperm concentration, two bacteria belonging to the Pseudomonas family were found in higher abundance (Pseudomonas fluorescens and Pseudomonas stutzeri).  The researchers also found a lower concentration of Pseudomonas putida in these men.


  • Overall, the men with atypical semen analysis had one bacterium in particular: Lactobacillus iners in higher abundance. It was more abundant in men with reduced sperm mobility, accounting for 9.4% of sperm bacteria compared with 2.6% in healthy men with no fertility problems.


Similar results had been demonstrated in women suffering from infertility. In a previous study, Lactobacillus iners was associated with a low success rate in MAP**. Its negative effect could be explained by its production of lactic acid, which promotes inflammation and could impair sperm motility.


According to their conclusions, these micro-organisms could have a positive or negative influence on men’s fertility. In fact, they could have an impact on the characteristics of spermatozoa, such as their number or mobility.


Although these are only correlations, these initial results nevertheless suggest that restoring the balance of the sperm microbiome could play a role in sperm quality and therefore in male fertility.



*WHO : World Health Organization

**MAP: Medically Assisted Procedures

OSADCHIY V, BELARMINO A, KIANIAN R, SIGALOS JT, ANCIRA JS, KANIE T, MANGUM SF, TIPTON CD, HSIEH TCM, MILLS JN, ELESWARAPU SV. Semen microbiota are dramatically altered in men with abnormal sperm parameters. Sci Rep. 2024, 14(1):1068.