Corrine Maurice, PhD: The Role of the Gut Microbiota

The gut microbiota is now an "essential organ," Corrine Maurice, PhD, an assistant professor in the department of microbiology and immunology at McGill University, explained during a presentation at the European Congress of Clinical Microbiology and Infectious Disease (ECCMID 2019). Maurice sat down with Contagion® post-presentation to discuss the interactions between host, bacteria, gut microbiota, and bacteriophages more in-depth.

Interview transcript (modified slightly for readability):

Contagion®: In your presentation, you stated that the microbiota is now an “essential organ.” Can you explain that a bit more?

Dr. Maurice: The work that my lab and myself are doing is working on the microbial communities that you find in the human gut, and so we call that the gut microbiota because it's essentially this collection of microorganisms that you'll find in the human gut. Most of the research to date on the human gut microbiota has really been focusing on bacterial communities and there's really a wealth of literature in the last decade or so that shows the role that these bacteria play in our health. They're really important in maintaining the energy balance for the human host and so this has implications for obesity, for example. The gut microbiota is also very involved in priming our immune system and making sure that we have the adequate immune responses. There have been a lot of papers that show that, for example, in allergy situations you really have strong changes in your gut bacteria. There are also examples of how the bacteria in your gut help you resist pathogen infection. That's called the colonization resistance. We don't quite know exactly how that works, but it's very clear that if you don't have a diversified gut bacterial community, you are at higher risk of acquiring these pathogen infections. Of course there are several examples and lines of evidence of the role of the gut bacteria in chronic inflammatory diseases, the most notable ones being inflammatory bowel disease, so that's Crohn's disease and ulcerative colitis, for example. These are just a few examples of very clear effects or roles that the gut microbiota may have. There have been more and more studies that show links between changes in the gut bacteria and other conditions that are not GI-tract located. There are links between changes in your gut bacteria and depression and autism, and that's been like put forward with the famous gut-brain axis that's been receiving a lot of hype.

There are also examples of links between the oral bacterial communities and the gut. In some cases we see bacteria that should be found in your mouth that, unfortunately when they make it to your gut, you seem to be at higher risk of developing some cancers, for example. With all these lines of evidence, it's been suggested a few times that basically when you're treating someone, you should really consider the gut microbiota and the gut bacterial communities because they will have a role for your health. There have been a few papers that have suggested basically to consider the gut microbiota as this organ that isn't a real organ that the doctors would look at per se, but clearly now you have to consider it when you are considering a disease or pathology. The work that I was presenting was basically arguing that, in addition to following the bacterial communities, you should also be following the bacteriophage or phage communities. These are viruses that only infect bacteria; they are not known to infect any human eukaryotic cell. The idea is that you should be also following these communities because they are as abundant as your bacterial cells. Very often we put forward the fact that bacterial cells are as abundant as our own human cells, in some cases up to 3 times more abundant, but in the case of phages you would have at least as many phages as your bacteria and these are the early estimates. Depending on how you count them, that number can increase to 10, so there could be 10 more phages than bacteria in your gut so obviously we just can't exclude them from our analysis.

Contagion®: Is it possible to manipulate the gut microbiota to treat certain conditions?

Dr. Maurice: Several teams are looking into manipulating the gut microbiota using antibiotics or other types of medication or, more simply put, through diet. All of these studies have showed very contrasted results but there are results, which really do put forward the fact that you can manipulate the gut microbiota. We're interested in using it and manipulating the gut microbiota in another way using phages because we know that they're naturally present there in the gut and every single known microbial community on earth where you have bacterial cells, you're going to have bacteriophages and they are known to control the abundance of the bacterial cells, their diversity and, in certain cases, what the bacterial cells are doing. Using that evidence from other systems, we're basically looking in the gut to see whether or not we can use phages for that exact purpose.

The symposium, "Ménage à trois in the human gut: interactions between the host, bacteria, and bacteriophages," was presented Sunday, April 14, at ECCMID 2019.