A new look at the human microbiome
One of the concepts that many health care students bring into Microbiology class with them is the unfortunate idea that the only “good” bug is a “dead” bug, and much of the discussion of infectious disease serves to forward this idea. Furthermore, it is often stressed (and I am as guilty of this as anyone) how many innocuous microorganisms become significant pathogens in health care situations, therefore we must be vigilant with our patients in order to prevent the development of nosocomially acquired infections.
I saw an interesting article in USA Today that did an excellent job of describing why we may actually be doing significant damage to our bodies with our emphasis on controlling microorganisms in our environment. I have written before about the “hygiene hypothesis,” which posits that our fastidious lifestyle renders us more susceptible to various forms of infection. Most recently here in BIO230, this was in the context of a preliminary epidemiological study in an Amish community, where exposure to many common microorganisms has potentially resulted in very low observed levels of many common childhood allergies.
The USA Today article describes of situations where our normal microbiota, or microorganisms that coexist with us as permanent residents of the human body in the absence of disease, actually appear to actively prevent other diseases. This in itself is not a new concept, however what appears to be the case is that the diversity of the normal microbiota is now being significantly altered by a number of environmental factors. As the ratio to one another of different organisms is altered by the prevalence of anti-bacterial chemicals and antibiotics, the benefits that those organisms confer on us are lost. For instance, there is evidence that Helicobacter pylori in the gut affects appetite by suppressing hormones that tell us that we’ve eaten enough. Decreases in H. pylori levels in humans have clearly helped to diminish the incidence of gastric ulcers and stomach cancer, however loss of H. pylori may also be linked with increases in childhood obesity.
Multicellular organisms including humans have developed a peaceful coexistence with their normal microbial flora over the course of millions of years. Humans acquire the vast majority of their flora from their mother, during the process of birth, and the presence of these organisms are critical for proper development during the first few months of life. Although mice can be maintained in a “germ-free” environment lacking a complement of normal microbiota, there is firm evidence that these animals are fundamentally abnormal to the point of demonstrating significant behavioral defects attributed to the lack of gut microorganisms.
So consider this next time you reach for the antibacterial soap: in addition to killing pathogens in your environment, you may also be killing the normal bacteria on you.
BONUS: In the comment thread, list a possible health benefit of the normal microbiota, beyond the behavioral benefits specifically noted above, or the link to obesity due to H. pylori. To help out, here is a Google search link. I will reward comments by bonus points in BIO230 class this summer!