Bacteria living in men’s penises could be promoting sexually transmitted infections

The debate about whether to circumcise or not continues to raise passions. The fact that male circumcision reduces acquisition of HIV from an infected partner has been proven by three randomised clinical trials. And male circumcision may also protect against other sexually transmitted infections.

One of the most powerful arguments against male circumcision is that it only addresses acquired infections in the male. A recent report in the Scientist that bacteria living under the foreskin can promote STI’s would help answer this critique.

Just as the vaginal microbiome differs among women and changes over time, the penis is home to a variety of bacteria that vary with age, sexual activities, and whether the man is circumcised, among other things. And it’s not just the skin that envelops the male sexual organ that’s inhabited by microbes: researchers continue to identify bacteria that dwell within the urogenital tract, a site once considered sterile in the absence of infection.

David Nelson and colleagues at Indiana University in Bloomington found evidence to suggest that the sexually transmitted pathogens in the urogenital tract were obtaining metabolites from other microbes. “There was a signature in the chlamydial genome that suggested this organism might be interacting with other microorganisms,” said Nelson. “That’s what initially piqued our interest. And when we went in and started to look, we found that there were a lot more [microbes] than we would have anticipated being there.”

The researchers found that some men pass urine containing a variety of lactobacilli and streptococci species, whereas others have more anaerobes, like Prevotella and Fusobacterium. In terms of overall composition, “we see a lot of parallels to the gut,” said Nelson, noting that there doesn’t seem to be a standout formula for a “healthy” urogenital tract. Commensal microbes within the urethra could make a man more susceptible to infection by supporting colonization by pathogens like Chlamydia, whereas bacteria that consume the environment’s nutrients could help prevent it. “We just don’t know at this point,” said Nelson.

To date, circumcision is the known largest influence on the composition of the penis microbiome. In a 2010 PLOS ONE paper, Lance Price of the Translational Genomics Research Institute in Phoenix, Arizona, and his colleagues showed that the bacteria that colonized the base of the penis’s tip, or glans, varied before and after circumcision. More specifically, the researchers found fewer anaerobic bacteria within six months after the men in a study were circumcised. Those findings have since been confirmed.

Definitely further studies in this field should be encouraged.

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