Sexuality: the secret life of the seminal-vaginal microbiota

During unprotected sex, thousands of microorganisms are also shared via semen and vaginal secretions. Yet for years, researchers have scrutinized the vaginal microbiota (which has been extensively studied) on the one hand, and the semen microbiota (which has been studied much less) on the other, as if they lived on two different planets. The idea that they might interact in a sexually active couple? Barely touched upon by 14 small studies.

Two very different worlds, but open to exchange

The seminal microbiota of men is completely different from the vaginal microbiota of women: it is generally more diverse, has a lower bacterial concentration, and a slightly alkaline pH of 7.5... whereas the vaginal microbiota is less diverse, dominated by lactobacilli, and has an acidic pH (a direct consequence of the abundance of lactobacilli, which secrete acids) .

However, unprotected sex means the exchange of fluids and bacteria. Female couples often share a similar vaginal microbiota. Male homosexual couples (men who have sex with men) are distinguished by a unique rectal microbiota, rich in Prevotella and less diverse than that of heterosexual men.

In heterosexual couples, these exchanges could have consequences for fertility. This is true for both women and men. For example, an increased abundance of Lactobacillus in the seminal microbiota would go hand in hand with more mobile and concentrated sperm, but also—on the flip side—an adherence of lactobacilli to sperm that would reduce fertility.

STIs and dysbiosis also on the menu

Unprotected sex contributes to the transmission of sexually transmitted infections (STIs) but also disrupts the balance of intimate microbiota (dysbiosis (sidenote: Dysbiosis An imbalance in the microbial community, characterized by reduced beneficial bacteria and increased harmful species, potentially leading to adverse health outcomes. ) ).

Take, for example, the dreaded bacterial vaginosis, linked to a decrease in Lactobacillus and an increase in bacteria such as Gardnerella vaginalis. In heterosexual women, the increase in vaginal pH induced by semen could be a triggering factor for imbalance. It is also important to note that circumcision alters the microbiota of the penis skin, reducing its diversity and the presence of bacteria associated with bacterial vaginosis. Whether this protects women is still a matter of scientific debate.

Assisted reproduction

The microbiota in semen and the vagina may also play a role in the outcome of IVF (sidenote: In vitro fertilization (IVF) A medical assistance technique for procreation where fertilization takes place in the laboratory, in a test tube (“in vitro”), and not in the woman’s uterus: eggs retrieved from the woman after hormonal stimulation are placed in a nutrient solution with sperm collected from the man. The embryos thus conceived in the laboratory will then be transferred to the future mother’s uterus via the vagina. If an embryo implants, the pregnancy begins. https://www.service-public.fr/particuliers/vosdroits/F31462
https://medclinics.com/fr/fiv/
https://www.fiv.fr/fecondation-fiv/ ) , with certain seminal (Acinetobacter) or vaginal (L. crispatus) bacteria being associated with a higher chance of success. Conversely, Prevotella and Porphyromonas bacteria in parents reduce the chances of success.

A couple's reproductive health therefore appears to be linked to the so-called semivaginal (sidenote: Microbiote séminovaginal L’ensemble des micro-organismes provenant des écosystèmes séminal et vaginal qui sont transférés et partagés entre les partenaires lors de rapports sexuels non protégés, s’influençant mutuellement et impactant la santé et les fonctions reproductives. ) microbiota, which is still largely unknown. It is high time to gain a better understanding of how these microbiotas interact, coexist, and sometimes clash. Because yes, in a couple, intimate microbiotas also share a life together.