Male infertility: are bacteria in semen involved?
What if some of the bacteria present in men’s semen were involved in their infertility? This is suggested by the results of a study published in early 2024, which looked into this microbiota. 1
Healthcare professionals section
Find here your dedicated section
About this article
When a couple has difficulty conceiving, the fertility of both partners is assessed. In men, a sperm analysis called a
(sidenote:
Spermiogram
An examination that evaluates the quality of a sperm sample, including its volume (average normal volume = 1.4 mL), pH (which should be equal to or greater than 7.2), sperm concentration (normally greater than or equal to 16 million per mL), sperm motility (at least 30% must be able to move progressively forward, rather than spinning around or not moving forward) and vitality (> 54%). Other factors are also taken into consideration, such as sperm morphology, the overall appearance of the sample and its viscosity.
For a given patient, a semen analysis can never confirm fertility or infertility; the person’s fertility potential also depends on several other parameters and the fertility potential of the person’s partner.
Source: WHO
)
is usually prescribed. Despite this examination, almost 1 in 3 cases of
(sidenote:
Male infertility
A disease most often caused by problems with ejaculation, the absence or low quantity of spermatozoa, or abnormal sperm shape (morphology) or movement (mobility).
Source: WHO
)
(sidenote:
Infertility
Disease of the male or female reproductive system defined by the inability to achieve pregnancy after 12 months or more of regular unprotected sexual intercourse.
Source: WHO
)
remain unexplained. But a new avenue is now being explored: that of the sperm microbiota.
L. iners, an anti-fertility bacterium?
As we all know, semen is far from sterile. It is home to a community of microorganisms, with the most numerous being the bacteria Enterococcus faecalis, Staphylococcus epidermidis, Corynebacterium tuberculostearicum and Lactobacillus iners. However, there are subtle differences associated with sperm quality. For example, in men whose sperm have difficulty moving forward (and therefore have difficulty reaching the egg), Lactobacillus iners bacteria are much more prevalent: they account for 9.4% of bacteria in semen, compared with 2.6% in men whose sperm have normal motility.
In a previous study, the high presence of this bacterium in women’s vaginas was associated with less successful medically assisted procreation (MAP). Its harmful effect could be explained by its pro-inflammatory qualities, which generally do not make for a very good nesting place for fertility!
Everything you always wanted to know about penile microbiota (but were afraid to ask)
Pseudomonas also involved
The 3 other bacteria singled out by the researchers all belong to the genus Pseudomonas, previously unknown to the fertility police: semen with a low sperm concentration is richer in Pseudomonas stutzeri and P. fluorescens, and less rich in P. putida. Researchers therefore suspect that the first two bacteria of this genus may go hand in hand with low fertility, while the latter could have a beneficial effect.
Of course, once again, these are only correlations, not cause-and-effect relationships. Nevertheless, these results suggest that these bacteria could play a role in sperm quality, and therefore male fertility. To be continued in future studies..I
1. Osadchiy V, Belarmino A, Kianian R et al. Semen microbiota are dramatically altered in men with abnormal sperm parameters. Sci Rep. 2024 Jan 11;14(1):1068.
2. https://www.who.int/health-topics/infertility
3. Levine H, Jørgensen N, Martino-Andrade A et al. Temporal trends in sperm count: a systematic review and meta-regression analysis. Hum Reprod Update. 2017 Nov 1;23(6):646-659. doi: 10.1093/humupd/dmx022.
4. Eisenberg ML, Esteves SC, Lamb DJ et al. Nat Rev Dis Primers. 2023 Sep 14;9(1):49.
