Penile bacteria, SEM

Bacteria from a penis. Coloured scanning electron micrograph of bacteria from an uncircumcised penis. The skin of the penis is home to a diverse community of bacteria. Genetic tests to identify the bacteria found on men's penises showed there were a total of 42 unique kinds of bacteria inhabiting the skin. Studies have shown uncircumcised and circumcised penises don't have the same variety and abundance of bacteria. After circumcision, there were fewer kinds of bacteria on mens penises. Many of the kinds of bacteria found to be less common or absent after circumcision were anaerobic (don't need oxygen to grow). Circumcision has been linked to a lower risk of contracting HIV (human immunodeficiency virus). One theory is the anaerobic bacteria may prompt the immune system to respond in a way that makes cells more vulnerable to HIV infection. Magnification: x6600 when printed at 10 centimetres wide.