The Microbiome: Linking Bacteria, Health, and Disease

Robert C. Rickert, PhD; Scott Peterson, PhD


June 19, 2013

Editorial Collaboration

Medscape &

In This Article

Connections Between the Microbiome and Colorectal Cancer

Dr. Peterson: A third example also involving the gut microbiome is a study we're involved in with Johns Hopkins University, in which we're studying the microbiome and its relationship to colorectal cancer.[2] The study design we're using there involves looking at the microbiome that is physically associated with colon tumors and comparing that with the microbiome that exists in healthy tissue flanking that tumor by a few centimeters. So we're within a single individual comparing physically close relationships of microbiomes. We see both tremendous similarities as well as some conspicuous differences, depending on whether the population is associated with a tumor or not.

We've identified a few unique species that appear to be associated with the tumor itself and not associated as strongly with the healthy flanking tissue. What we don't know, and what oftentimes gets to be a problem with microbiome research, is the chicken-and-egg issue. Does the change that we observe reflect the fact that there's a disease state, which then alters the environment and the microbial population that's resident there? Or does the change in the microbiome population have some influence on the progression or onset of a disease? That's a question that I think we'll wrestle with over the next several years.

Dr. Rickert: So it seems to be a 2-way street -- the microbiome is affecting the tumor, and vice versa?

Dr. Peterson: Right. One of the important things -- and I think of it as a consolation prize -- is that we win either way, because we also have interest in finding diagnostic biomarkers for disease.

The dental caries issue is a very good example. In these longitudinal studies, we see the progression of events that lead to a caries-active state. So we can start to define molecular markers -- proteins, RNA, or DNA -- that represent early stages of disease onset. For colorectal cancer, it's a lot more difficult to do longitudinal studies, but we still have this notion that we can use the bacterial populations as a set of biomarkers that could potentially represent very early diagnostic indicators.

We have really good reason to believe that these will be powerful tools, because we know that bacteria are extraordinarily responsive to their environment. Their fitness is easily affected by just small changes in the microenvironment. So the idea that a disease state could influence what's selectively advantageous in terms of that microbial population becomes something very plausible for us to hopefully find early diagnostics that could save a lot of lives.