In this rather long article in Nature, Sujata Gupta writes about researchers who are trying to figure out why some intestinal infections become the chronic disorder Irritable Bowel Syndrome. The section on the research of pathophysiologist Andre Buret at the University of Calgary, Canada, I found particularly interesting.
Gut bacteria inhabit a harsh environment that is subject to constant flushing and exposure to foreign substances. To survive, the bacteria create communities known as biofilms that are coated with protective polysaccharides. Buret wondered whether some pathogens might modify these bacterial films, inducing abnormalities that persist after the pathogen is gone. To test this idea, he put some microbial samples in a dish and infected them with Campylobacter and Giardia.
Buret's team found that Giardia and Campylobacter disintegrate the protective biofilms, so the once-beneficial bacteria can move to other parts of the gut where they become disruptive. Buret has also shown that these pathogens can alter the gene expression of freed gut bacteria, making them toxic. This interaction, he says, “transforms them into pathobionts” — the bacterial equivalent of zombies.
Like their human equivalents, zombie bacteria wreak havoc. In an unpublished study on germ-free mice, Buret found that these pathobionts target and kill the cells of the small intestine. Long after the instigating pathogen has gone, the actions of the pathobionts continue to cause gut inflammation. And with no way to get rid of the zombie menace, the inflammation can persist indefinitely.