Scientists have mapped out for the first time the bacterial landscape of the human body.
Writing in Science, University of Colorado at Boulder researcher Rob Knight and his colleagues collected swabs from 9 individuals on four occasions sampling in each the same 27 sites including the skin, hair, mouth, gut genitals and face.
Using DNA analysis they were able to identify the different bacterial groups inhabiting each of these sites and to compare the bacterial profiles both in the same individual and between individuals on all four occasions. Surprisingly, the team's results showed that the mouth microflora showed the least variability both within an individual and among individuals, whilst the skin showed dramatic variability - greater even than the gut - from one part of the body to another in each individual. There were some general trends that emerged too; the face tended to be heavily populated by Propionibacterial species while the trunk and legs were more heavily colonised by Staphylococci or Corynebacteria.
To find out what might be contributing to these "biogeographic" patterns the team then carried out bacterial transplantation experiments. Patches of skin on one part of the body were first sterilised with alcohol and then bugs from another part of the body - or even another person's body - were rubbed on.
Applying mouth bacteria to the forearm lead to a shift in the kinds of bacteria growing on the skin, but the same transfer from mouth to forehead very rapidly led to a return to more forehead-like bacterial cross-section.
These results show that body habitat makes a dramatic difference to the spectra of bacteria that can thrive and colonise certain sites. Above all, this is the first time that a comprehensive "whole body" assessment has been made of the human microflora, which outnumber our own cells 50 to 1. The researchers suspect that disruption to these normal states might underlie or provoke certain disease states, but first they have to know what's normal to register what might be going wrong.
"This is the most complete view we have yet of the microbial side of ourselves," says Knight. "The goal is to find out what is normal for a healthy person, which will provide a baseline for further studies to look at people with diseased states."