There’s a good short piece, Humans Have Ten Times More Bacteria Than Human Cells: How Do Microbial Communities Affect Human Health?, in Science Daily, picks up on some of the themes we discussed in The human ’super-organism.’ The overwhelming majority of cells in human bodies belongs to microbes — the article says 10 bacteria cells for every human body cell (does it make you feel tired to think how much bacteria you’re carrying around?). Recognizing that we are a shambling micro-cosmos of oraganisms (or ‘microbiome’) suggests new understandings of all sorts of things, including disease. The Science Daily article points out that ‘changes in these microbial communities may be responsible for digestive disorders, skin diseases, gum disease and even obesity.’
There’s one passage in particular that I thought was worth posting, even if I don’t have too much to add:
“This could be the basis of a whole new way of looking at disease. In order to understand how changes in normal bacterial populations affect or are affected by disease we first have to establish what normal is or if normal even exists,” says Margaret McFall Ngai of the University of Wisconsin, Madison.
The microbiome research is particularly interesting to us at Neuroanthropology, even though it’s not strictly about the brain or nervous system, because it’s a particular compelling demonstration that the human body is a dynamic system; that is, the body is a system of different forces and processes, at a number of scales, that together continually produce the whole, sometimes in equilibrium and sometimes in ways that produce dysfunction.
Studies of microbes on the skin have found that around 50% belong to ten species, but some bacteria are specific even to a single person: “What was interesting about some of the other species with smaller populations is that they were host specific. We could only identify them on a single host. It is entirely possible that everyone could have a unique bacterial signature,” says Martin Blaser of New York University. Blaser has gone on to study the epidermal microbiome of patients with psoriasis and found that they have distinctive bacterial populations (the article doesn’t even hazard to suggest whether these differences might be cause or effect of their skin conditions).
Recognizing its importance, the National Institutes of Health in December 2007 announced the Human Microbiome Project as part of its Roadmap for Medical Research, devoting over $100 million in grants over the next five years.
In particular, the research will target five regions of the body: the skin, mouth, gastro-intestinal tract, nose, and female urogenital system.
To my knowledge, there’s not really a focus on the idea that different human populations might support different microbial populations. The account in Science Daily seems to focus exclusively on the contrast between ‘normal’ and disordered or diseased. Although I heartily support the research, and just can’t wait to check out the cool results, I would simply echo Ngai’s caveat that we don’t know ‘if normal even exists.’ I’m betting, especially reading some of the material from Blaser about idiosyncratic species, that ‘normal’ is likely to be pretty hard to pin down.
Scanning electron microscope images of B. thetaiotaomicron, human gut bacterium, and the intestine. Photo from PLoS Biology 2007 July; 5(7): e199. Published online 2007 June 19. doi: 10.1371/journal.pbio.0050199. Found at Baylor College of Medicine’s website.
Thanks to Bora Zivkovic at A Blog Around the Clock for putting me onto the original Science Daily article. Bora, you’re a blogging machine.
American Society for Microbiology. 2008 (June 5). Humans Have Ten Times More Bacteria Than Human Cells: How Do Microbial Communities Affect Human Health?. ScienceDaily. Retrieved June 7, 2008, from http://www.sciencedaily.com /releases/2008/06/080603085914.htm