Removing the foreskin causes a significant shift in the bacterial community or microbiome of the penis, a new study has revealed.

Male circumcision reduces the abundance of bacteria living on the penis and might help explain why circumcision offers men some protection against HIV, according to a study led by the Translational Genomics Research Institute (TGen).
This international collaboration focused on 156 men in Rakai, Uganda - part of the world`s largest randomized-controlled trial on male circumcision.

Researchers showed that men who were circumcised as part of the study had 33.3 percent less bacteria on their penis than those who remained uncircumcised one year after the study began.

Researchers further showed that the decrease was primarily found in 12 types of bacteria, most of which were intolerant to oxygen.

Past studies have shown that circumcision reduces female-to-male HIV transmission, among other benefits.

This study suggests a possible mechanism for HIV protection - the shift in the number and type of bacteria living on the penis.

Further studies will have to be done to demonstrate that a change in the penis microbiome can help reduce the risk of HIV transmission, according to the authors.

At the same time, understanding the mechanisms that underlie the benefits of male circumcision could help to identify new intervention strategies for decreasing HIV transmission, especially for populations with high HIV prevalence and in places where male circumcision is culturally less acceptable, the study says.

"We know that male circumcision can prevent HIV and other diseases in heterosexual men, but it is important to know why," Dr. Lance Price, the Director of TGen Center for Microbiomics and Human Health and the study`s senior author said.

"We think that these dramatic changes in the penis microbiome may explain, at least in part, why male circumcision is protective," he said.

The study is published online in the journal mBio.