The Microbiome: Linking Bacteria, Health, and Disease

Robert C. Rickert, PhD: Hello. I'm Dr. Robert Rickert, Professor and Program Director in the Infectious and Inflammatory Disease Center at Sanford-Burnham Medical Research Institute. Welcome to this segment of Developments to Watch, from Sanford-Burnham and Medscape.

Today, I will be talking to my colleague, Dr. Scott Peterson, Professor in the Center, about the work that he and his team are doing in studying the interactions between the microbiome and health and disease.

Now that many of the trillions of microbes that live in the human body have been characterized and categorized, Scott and his team are working in a variety of settings to try to understand how these microbes influence normal and abnormal human conditions -- from changes in body weight to cancer -- and are looking for ways to use this information to improve human health.

Scott, could you tell us what roles microbes play in keeping us healthy?

Scott Peterson, PhD: That's a very refreshing question, because so much of the focus now in the human microbiome research area has to do with its role in disease. In my way of thinking, that is only just half the story.

The answer to that question is still largely unknown. We don't fully appreciate the details of what makes microbes keep us in a state of health. But what we do understand is that for them to occupy our bodies and live in concert with us as their human host, microbes need to pay their dues. They need to either supply us with something that's beneficial, or they need to support other bacteria that live in or on our bodies to enable their existence and selection to coexist with us. It's through that set of assumptions that these organisms are living in a mutualistic relationship with us, and on that basis we assume -- and I think rightly so -- that they're providing a health benefit.

We have some limited number of examples so far. We know that there are certain vitamins that microbes make -- xenobiotics, probiotics -- that provide a health advantage to the human host. But we largely don't understand the details of how deep that health benefit goes.

The dental community was among the first to really appreciate the role of the microbiome (although it wasn't called that), with the idea of polymicrobial disease and the impact of microbes on dental caries. Association studies more recently revealed, maybe for the first time, that humans who were in a caries-free health state had certain species of bacteria that were more abundant or more prevalent than in those who were caries-active and in a state of disease.

Dr. Rickert: So there were clear disease associations?

Dr. Peterson: That's right. This is what we really need to appreciate. The fascination and the real power of this notion of human health in the microbiome relationship stems from the fact that we know that microbes and the genes that they encode are enormously diverse -- oftentimes, through biochemical pathways that are unique to a particular species and not expressed in any other life forms. When we consider that the human genome has something on the order of 30,000 genes encoded, the typical microbiome in a particular body site, such as the oral cavity or the human gut, will encode 3 million to 10 million genes.

So we really have an enormous capacity for expression of genes and potential therapeutic compounds coming from the microbiome. This is what I hope to focus my attention on -- not only disease, but also the potential for harvesting the health benefits of the microbiome.

Dr. Rickert: Can you give us some examples of your current research?