Researchers have successfully mapped the different microbial communities over the whole body according to research by Costello and colleagues published in Science this week.
The human body is home to trillions of bacteria, so many that in fact bacteria outnumber our own cells by 10 to 1. The human body’s microbiota (the microorganisms that live inside or on our body) is often diverse and complex. It is important to examine the different communities of bacteria that live in association with a healthy human body so that we can better understand how these microorganisms affect our health.
The researchers assessed the diversity of bacteria in different habitats on the body, in different people and whether these bacterial communities changed over time. Over the course of three months, the researchers surveyed and sequenced the different bacteria from up to 27 human body sites – including the ear canal, gut, mouth and skin – in seven to nine healthy adults. They found that bacterial communities were defined by their location on the body. Some body sites, like the back of the knee or the gut, have many different types of bacteria living there whilst places like the navel or forehead have very few types of bacteria. These bacterial communities within each habitat varied little over time in individuals. Surprisingly, some skin sites – including the forearm, palm, index finger and back of the knee – had a greater diversity of bacteria compared with the gut and the mouth (body sites known to harbour many different types of bacteria). The researchers then “transplanted” bacteria from one site on the body to another (after sterilisation) and monitored which bacteria grew to test whether some parts of the body were more hospitable to bacteria than others. For instance, tongue bacteria could grow on a person’s forearm but not on their forehead and similar results were achieved when transplanting one person’s tongue bacteria onto another person’s forearm or forehead. Finally, the researchers found that different people had very different types of bacteria living on them (we have our own personalised set of microorganisms living on us).
Further work is needed to survey the human microbiota of more people and how it changes over a longer period of time. Studies like the Human Microbiome Project will help to map the microbes of many more people and further our understanding of the microbial factors which are associated with health and disease.
Costello, E., Lauber, C., Hamady, M., Fierer, N., Gordon, J., & Knight, R. (2009). Bacterial Community Variation in Human Body Habitats Across Space and Time Science, 326 (5960), 1694-1697 DOI: 10.1126/science.1177486