The Microbes of Men

Staphylococcus, one of the types of bacteria identified in the study.Matthew J. Arduino, CDC

A new study revealed a surprisingly diverse and stable community of microbes in the male urinary tract and on the penis. The findings will help lead to a better understanding of male reproductive and sexual health.

Scientists have become increasingly interested in the diverse microbial species living in and on the human body. Some of these bacteria, fungi, protozoa and viruses cause illness, but many benefit our health. There's strong evidence that the microbial communities in the female reproductive tract affect reproductive health and resistance to infectious disease. The microbes of the male reproductive tract, in contrast, aren't well understood.

A team of researchers led by Drs. David E. Nelson and J. Dennis Fortenberry of Indiana University examined the microbial communities of the male urinary tract (urethra) and penis. They enrolled 18 young men (ages 14–17) and asked them to fill out a questionnaire about circumcision, sexual activity and any genital or urinary symptoms. The scientists collected urine samples and swabbed an exterior area of the penis called the coronal sulcus. They then took samples 3 more times at 1-month intervals.

To analyze microbial diversity, the team sequenced and compared ribosomal RNA (rRNA) from the samples. rRNA is a central component of the protein manufacturing machinery of all living cells, and is often used to analyze bacterial communities. NIH's National Institute of Allergy and Infectious Diseases (NIAID), National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) and National Human Genome Research Institute (NHGRI) funded the work. Results appeared on May 11, 2012, in the online journal PLoS One.

The scientists found that both the urinary tract and the coronal sulcus support stable and distinct bacterial communities. Researchers hadn't previously known that pre-sexually active men harbored bacteria in their urinary tracts. Urine contained different bacteria than the coronal sulcus. Most common in urine were Streptococcus, Lactobacillus, Gardnerella and Veillonella. The microbes in urine varied more within participants over time than those from the coronal sulcus.

Bacterial populations on the coronal sulcus were significantly affected by circumcision, but those in urine weren't. Staphylococcus was enriched on the coronal sulcus of circumcised participants, while Porphyrmonas was enriched in uncircumcised participants. Prevotella was found only in uncircumcised participants. Male circumcision is known to reduce the risk of acquiring HIV and other sexually transmitted diseases. This finding suggests that microbes may play a role in these protective effects.

Sexual activity affected the microbial communities as well. No known sexually transmitted organisms were detected in the study. However, certain microbes—including Sneathia, Mycoplasma and Ureaplasma—were detected only in sexually active participants.

This research will help scientists understand the role that microbes play in men's health. “We have some sense that some of the bacteria in the urethra are essential to keeping men healthy,” Fortenberry says. “This research and the new technology will open doors to explore what is good about the bacteria, what they do and how.”

The researchers plan to follow these and other adolescents for several years to determine how the types and amounts of bacteria change over time.

—by Harrison Wein, Ph.D.