Study: key bacteria in gut can promote foodborne illness

Ecoli_resizedAlthough many think the worst when they hear “E. coli,” there are many forms of the bacteria that are actually harmless and critical to gut health. However, one of the most harmful forms is known as enterohemorrhagic E. coli (EHEC) which causes diarrhea and is linked with outbreaks featured in the news, including this year’s multistate outbreak tied to raw sprouts and ground beef.

Scientists recently discovered that what makes this type of E. coliso dangerous is that it is able to hijack those otherwise harmless forms of bacteria in the gut to worsen its infection and spread intestinal illnesses.

According to a recent article, a team of researchers found that that EHEC uses a common gut bacterium called Bacteroides thetaiotaomicron (B. thetaiotaomicron), a predominant species in the gut’s microbiota, which consists of tens of trillions of microorganisms used to digest food, produce vitamins, and provide a barrier against harmful microorganisms.

“EHEC has learned to how to steal scarce resources that are made by other species in the microbiota for its own survival in the gut,” lead author Dr. Meredith Curtis, postdoctoral researcher at University of Texas – Southwestern said in the article.

The article goes on to say that the research team found that B. thetaiotaomicron causes changes in the environment that promote EHEC infection, in part by enhancing EHEC colonization.

“We usually think of our microbiota as a resistance barrier for pathogen colonization, but some crafty pathogens have learned how to capitalize on this role,” said Dr. Vanessa Sperandio, professor of microbiology and biochemistry at UT Southwestern and senior author.

The team found that EHEC is able to do this by sensing changes in sugar concentrations brought about by B. thetaiotaomicron. EHEC then uses this information to turn on virulence genes that help the infection colonize the gut, prevent recognition by the host’s immune system, and obtain enough nutrients to survive.

As stated in the article, the group observed a similar pattern when mice were infected with their equivalent of EHEC, the gut bacterium Citrobacter rodentium (C. rodentium). Mice whose gut microbiota consisted solely of B. thetaiotaomicron were more susceptible to infection than those that had no gut microbiota. Once again, the research group saw that B. thetaiotaomicron caused changes in the environment that promoted C. rodentium infection.

“This study opens up the door to understand how different microbiota composition among hosts may impact the course and outcome of an infection,” said Dr. Sperandio. “We are testing the idea that differential gastrointestinal microbiota compositions play an important role in determining why, in an EHEC outbreak, some people only have mild diarrhea, others have bloody diarrhea and some progress to hemolytic uremic syndrome, even though all are infected with the same strain of the pathogen.”

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