New findings on gut microbiome's interactions with GI diseases

In a study published on Oct. 31 in PLOS ONE, Amanda Blake, a doctoral student with the CVM's Gastrointestinal Laboratory, measured the levels of bacterial metabolic products -- fecal lactate and secondary bile acids (BA) -- in the fecal matter of dogs with different gastrointestinal (GI) conditions.

Fecal lactate and secondary BA are both substances made by bacteria, and the concentrations at which they are present in fecal matter can inform researchers about the activity of bacteria in the GI tract. The different levels of these substances in a diseased host vs. a healthy host can inform researchers of how GI bacteria act in diseased vs healthy environments, as well as how GI bacteria interact with different diseases.

In her study, Blake found higher levels of lactate and lower levels of secondary BA in the feces of dogs with chronic enteropathy (CE) and dogs with exocrine pancreatic insufficiency (EPI). This is noteworthy since, although these two diseases have different symptoms and causes of disease, the bacterial outputs of their gut microbiota appear to be similar.

"The goal was to look at the bacteria and then also products that the bacteria make. These metabolites, which are lactate and secondary bile acids, reveal similarities across GI diseases that are very different physiologically," Blake said.

These findings can help the community better understand interactions between GI microbiota and disease.

By focusing on the metabolic products of an affected animal, Blake's research is unique in that it accounts for not only the types of bacteria present, but also how these bacteria are interacting with their environment. This is important because the same species of bacteria can produce different products dependent on the health of their environment. A particular species of bacteria in a healthy animal might produce a different chemical than it would in a host with a GI disease.

"If we can find ways that the microbiota interacts with the host and we can compare between health and disease states, then maybe we can alter some of those interactions in disease to make the microbiota healthy and then hopefully make the individual healthy in the end," Blake said.

Currently, treatments for many GI afflictions are non-specific, which might be of more harm than help for the animal. Better understanding the GI microbiome would allow researchers to develop more targeted treatment options.

"Sometimes the inconvenience of a symptom like diarrhea leads to veterinarians to throw everything at the dog: the antibiotics, the steroids. Give it everything, and hopefully one of them will make it stop," Blake said. "We're finding more and more that giving dogs these medications unnecessarily can actually change their microbiota for the worse."

These findings could also be relevant to treating similar GI conditions in human patients.

"Humans also get exocrine pancreatic insufficiency, and chronic enteropathy in dogs is similar to inflammatory bowel disease (IBD) in humans," Blake said. "A lot of people know what IBD is for human medicine, or Crohn's disease. The same findings could be applied to humans with those GI diseases."

Blake emphasizes that an open view on the functions of different species of bacteria is best, and that researchers should be hesitant about labeling certain species as definitively helpful or harmful.

"It's not good guys and bad guys for the microbiota," Blake said. "We need to pay attention to a combination of factors, such as their environment, the metabolic products that they're making, and the individual patient to better understand the role of microbiota in disease."