The seminal microbiome describes microorganisms found in semen. Studies have explored associations with sperm concentration, motility and morphology, while the proposed gut–testis axis concerns communication between intestinal microbes and reproduction. Human associations and animal experiments offer different kinds of evidence; neither alone establishes a fertility treatment.
Male infertility assessment includes more than sperm count, motility and morphology. The EAU guideline also includes medical and reproductive history, relevant lifestyle factors and physical examination. Microbiome research asks whether microorganisms add useful information to this broader assessment.
The seminal microbiome and reported sperm-quality associations
One area of investigation is the seminal microbiome: the microorganisms present in semen and their possible relationship to reproductive health.
In a 2019 observational study by Baud and colleagues, semen from 94 men at Lausanne University Hospital was examined using bacterial sequencing. Prevotella-enriched, Lactobacillus-enriched and mixed profiles were identified. Overall community composition did not distinguish semen-quality groups.
Specific associations varied: that study linked more Prevotella with impaired motility and more Lactobacillus with normal morphology. Yet a 2024 UCLA-led study of 73 men associated greater Lactobacillus iners abundance with abnormal motility. A genus cannot therefore be labeled universally beneficial or harmful; these studies did not establish microbial causation or a DNA-damage diagnostic fingerprint.
The proposed gut–testis axis
The proposed gut–testis axis is a related but separate question. In a 2024 mouse study by Argaw-Denboba and colleagues, disrupting paternal gut microbes altered reproductive signaling and sperm RNA, with adverse offspring outcomes. Restoring the microbiota before conception reversed those effects in that model. This does not demonstrate the same effect or treatment in people.
These findings raise a useful clinical question: which microbial measurements, if any, improve decisions beyond established assessment? A semen association, an animal mechanism and a proven benefit for couples are separate steps. Studies need to test whether using this information changes outcomes, rather than only whether bacteria and sperm measures differ.
Probiotics and treatment claims: an early research area
Probiotics and microbiome interventions remain under investigation. The EAU guideline notes small trials with semen-parameter improvements but no conclusive overall benefit, and advises against routine prebiotic or probiotic treatment for idiopathic infertility. An improvement in sperm measurements does not itself establish a higher live-birth rate or justify choosing a particular commercial product.
Research sources and limits
Human studies: Baud et al., Frontiers in Microbiology (2019), doi:10.3389/fmicb.2019.00234; Osadchiy et al., Scientific Reports (2024), doi:10.1038/s41598-024-51686-4. Both compare microbes with semen findings; neither is a treatment trial demonstrating improved pregnancy or live birth. Animal experiment: Argaw-Denboba et al., Nature (2024), doi:10.1038/s41586-024-07336-w. Mouse results require human validation.
Related reading
Disclaimer: This content is provided for informational purposes, based on reporting on infertility and various public data. Medical judgments and treatment decisions must always be made in consultation with professional medical personnel. Image: AI-generated (ChatGPT, OpenAI) / Visual reference for illustrative purposes only.