Rapid advances in computational and genetic tools have allowed researchers to delve into the mystery that is the human gut microbiome. There are trillions of microbes in the human gastrointestinal tract that are intimately connected to various aspects of our physiology. While that is well established, scientists have been working to determine exactly which species of bacteria (or fungi, or viruses, for example) are associated with specific disorders. They have also been looking for reliable ways to modify the microbiome to alleviate some of those disorders.
While all of this is still a work in progress, scientists are learning new information all the time. Reporting in Cell Host & Microbe, investigators have now identified specific strains of gut bacteria that are linked to a bowel condition called inflammatory bowel disease (IBD), a term often used to describe the gut disorders Crohn's disease and ulcerative colitis.
IBD is becoming more common. This work could help scientists develop new tools to diagnose and treat the condition.
"Inflammation imposes tremendous selective pressures on gut bacteria, and so we hypothesized that the gut microbiome could contain unique bacterial lineages that not only become more abundant but are genetically adapted to these inflammatory disease conditions," said lead study author Adarsh Kumbhari, PhD, a research fellow in Medicine at Massachusetts General Hospital (MGH).
The researchers wanted to find bacterial strains in IBD patients that could help us understand the mechanisms underlying the disease.
Genetic tools can be used to identify the species of microbes in a fecal sample, which is often used to assess the state of the gut microbiome. In this work, the investigators determined exactly which bacteria tended to live in the guts of IBD patients, and which were usually found in healthy controls. They assessed fecal samples from patients and controls over time.
While the microbial composition of a healthy gut microbiome can vary significantly from one person to another, there are usually trends. Certain bacterial strains are known to promote good health, while others trigger inflammation or infection and the breakdown of the gut lining, That breakdown can lead to additional health problems if parts of the gut microbiome, such as microorganisms or the bioactive compounds they generate, escape the gut.
This study showed that certain bacteria are more prevalent in IBD patients compared to unaffected people, and these IBD-associated strains have evolutionary links to the disorder. The researchers also determined that strains of bacteria that promote disease tended to outcompete healthy bacteria when inflammation flared. The investigators suggested that this means that certain bacteria are genetically more likely to survive in a gut affected by IBD.
The bacteria that thrived during inflammatory bouts also showed genetic signs of promoting oxidative stress and immune system evasion.
"We also found that the loss of health-associated strains predicted higher fecal levels of calprotectin, a marker of inflammation severity," said senior study author Christopher S. Smillie, PhD, of the Center for Computational and Integrative Biology at MGH. "Our findings could have diagnostic utility and also have the potential to guide tailored interventions for IBD and other immune-mediated diseases."
Sources: Massachusetts General Hospital, Cell Host & Microbe
