Randomized controlled trials show that circumcision reduces the risk of HIV infection in men by 50-60% and reduces the risk of infection with human papillomavirus and herpes simplex virus type 2, but the biology behind these benefits is not well understood. It could be that the anatomy of the circumcised penis helps prevent infection, or it could be that changes in the microbiome confer protection, or some combination of the two.
Using swab samples from a large circumcision trial in Uganda, Price and his colleagues at Johns Hopkins and TGen set out to determine whether circumcision significantly alters the penis microbial community. Using a quantitative technique called qPCR along with pyrosequencing to identify individual community members, the researchers compared samples from uncircumcised men with samples from circumcised men that were taken both before the procedure and one year later.
“There was a dramatic and significant change in the penis microbiome as a result of male circumcision,” says Price. At the beginning, the microbiota of both groups of men were comparable. One year after their operation the bacterial load in all men had declined somewhat, but in circumcised men the decline was significantly greater than in the uncircumcised controls. And nearly all the bacterial groups that declined were strict anaerobes or facultative anaerobes. Overall, these changes amount to a reduced biodiversity in the microbiota.
This certainly makes sense. The foreskin overlapping on areas on the penis would deprive the area of oxygen creating an environment where anaerobic bacteria exist. Once it is removed oxygen is able to reach all areas of the penis making it inhabitable for for anaerobic bacteria.
I remember reading something about the foreskin having more receptors for the HIV virus as well….