Why do some foodborne bacteria make us sick? A paper published Sept. 16 in the journal Science has found that pathogens in the intestinal tract cause harm because they benefit from immune system responses designed to repair the very damage to the intestinal lining caused by the bacteria in the first place.
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A healthy large intestine is mostly free of oxygen, and the beneficial microbes residing there thrive in this anaerobic environment. In contrast, enteric pathogens, such as Escherichia coli in humans or Citrobacter rodentium in mice, need oxygen to survive.
Bäumler's team discovered how these pathogens change the gut environment to favor their own growth.
"Enteric pathogens deploy virulence factors that damage the intestinal lining and cause diarrhea," Bäumler said. "To repair the damage, the body accelerates the division of epithelial cells that form the intestinal lining, which brings immature cells to the mucosal surface. These new cells contain more oxygen and wind up increasing oxygen levels in the large bowel, creating an environment that allows gut pathogens like E. coli to outcompete the anaerobic-loving resident microbes."
