Saturday, January 9, 2010

What lives in foreskin

The range of bacteria that live in and around our bodies is striking. With the advance of molecular techniques and the ability to isolate organisms that traditional methods had huge problems detecting, we're learning more and more about what lives where. More importantly, how these symbiotic organisms affect us, both in terms of protecting us from or predisposing us to, various diseases, is going to be a tremendous growth area both for research and therapeutics over the coming years. We've already begun to alter the normal microflora, sometimes to good effect, like in the guts of premature babies to prevent them from getting infection, or to bad effect, like with antibiotic-related diarrhea.

Moving beyond the expected micro-organism dense area that is the human digestive tract, two recent papers in PLOS One look at the bacterial communities in two other parts of the human body: the penis and the lungs. The first is based on the now well-proven concept that circumcision is protective against sexually transmitted infections, and most tantalizingly, HIV. The theory behind this is under dispute, and the practicality of this as a population-level intervention still needs to be defined, but this paper lends even more biologic credence. There's reasonable in vivo evidence that HIV infection, in the presence of some specific bacteria, is more robust. Taking this piece of data, these authors show that circumcision drastically changes the microbial community isolated from the distal shaft of the penis. As fully expected, but never proven, the numbers of anaerobic bacteria, or bacteria that can live in oxygen-depleted environments, drops after circumcision, which is intuitive. In addition to the prevailing theory of decreasing the HIV-infected lymphoid cells in the penis region, this may help explain the significant effect circumcision has on HIV transmission, since the altered environment may not be as cozy an environment for the virus to live.

The second looks at the lower airways of asthmatics, which have long been thought to be mostly sterile. With newer molecular techniques, the authors isolated a host of micro-organisms, finding a fairly significant difference between sick and healthy lungs in the lower airway micro-environment. This time, the sick lungs had higher concentrations of a group of bacteria called proteobacteria, bugs that have been implicated in a number of respiratory illnesses in the past.

Moving forward, we still don't have the molecular basis for why having a different microflora effects whether or not we humans get disease. Both of these studies had very small numbers, and only looked at one geographic region, making generalizing specifics from these investigations challenging. Obviously, however, environmental factors have a large impact, since every person on the planet is exposed to different environmental micro-organisms throughout their life. Genetic factors will also be found to play a large role. Large-scale integration of human microbiome data with available human genome data, with attempts to figure out which host genetic factors lead to host colonization will be tremendously useful, but are still a work in progress. We're beginning to grasp the genetic susceptibilities to infection; what's next is integrating the genetic susceptibility to colonization, and figuring how that relates to human disease.


Price, L., Liu, C., Johnson, K., Aziz, M., Lau, M., Bowers, J., Ravel, J., Keim, P., Serwadda, D., Wawer, M., & Gray, R. (2010). The Effects of Circumcision on the Penis Microbiome PLoS ONE, 5 (1) DOI: 10.1371/journal.pone.0008422

Hilty, M., Burke, C., Pedro, H., Cardenas, P., Bush, A., Bossley, C., Davies, J., Ervine, A., Poulter, L., Pachter, L., Moffatt, M., & Cookson, W. (2010). Disordered Microbial Communities in Asthmatic Airways PLoS ONE, 5 (1) DOI: 10.1371/journal.pone.0008578

2 comments:

  1. The most compelling explanation for the effect circumcision has on HIV transmission comes from idnetifying who exactly is doing the research. When a certain group of long-time circumcision justifiers is involved the results are beyond belief.

    In the real world, most of the US men who have died of AIDS were circumcised at birth. The US - with excellent eductation and 80% of adults circumcised - has three times the HIV infection rate that Europe has, even though circumcision is rare in Europe.

    Foreskin amputation is obviously neither neccessary nor sufficient to thwart HIV.

    Condoms prevent AIDS better than anything short of abstinence.

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