Good Bacteria Can Limit E. Coli, Salmonella Infections


Scientists may have discovered the first step in combating the dangerous effects of bacteria-related infections, including salmonella and E. coli, according to a new study in the journal Nature.

The study investigates the effect of small protein molecules called microcins – produced naturally by healthy bacteria found in the intestines – on symptoms related to salmonella and E. coli.

Credit: NIAID/Flickr, CC BY 2.0

People affected by salmonella and E. coli bacteria, which have been at the center of recent disease outbreaks, experience intestinal inflammation, which often leads to diarrhea, abdominal cramps, fever and other symptoms.

But the microcins produced by healthy gut microbes can effectively block the dangerous bacteria from spreading, reports Manuela Raffatellu, Associate Professor of Microbiology and Molecular Genetics at the University of California, Irvine, and colleagues.

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“Although an in vivo role for microcins has been suggested for 40 years, it has never been convincingly demonstrated,” explained Raffatellu. “We hypothesize that their role was missed because, as our data indicate, microcins do not seem effective in noninflamed intestines. In contrast, we show that in an inflamed intestine, microcins help a probiotic strain limit the growth of some harmful bacteria.”

Preventing Bacteria-Driven Health Outbreaks

The researchers’ efforts may have a profound effect on public health if they can refine and reproduce their findings. Foodborne illnesses affect 48 million people in the United States every year, according to the Centers for Disease Control and Prevention (CDC).

Salmonella is considered the leading cause of death related to foodborne illness, according to CDC statistics. Also, harmful E. coli bacteria, often transmitted through contaminated food or water, routinely leads to illness in the U.S.

Last year, a widespread E. coli outbreak at Chipotle restaurants led to massive losses for the company, from which it is still trying to recover, according to reports.

However, not all E. coli is bad for you – in fact, most of it is healthy. E. coli bacteria “normally live in the intestines of people and animals,” states the CDC. “Most E. coli are harmless and are an important part of a healthy human intestinal tract,” though the agency adds that “some E. coli are pathogenic, meaning they can cause illness, either diarrhea or illness outside of the intestinal tract.”

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That’s where the work of Raffatellu and her colleagues comes in. For the study, they showed that a probiotic, or healthy, form of E. coli called Nissle 1917 “utilizes microcins to inhibit the pathogen salmonella and an invasive form of E. coli.”

“Our work provides the first evidence that microcins mediate inter- and intra-species competition among the Enterobacteriaceae in the inflamed gut,” wrote the study’s authors.

In other words, the good E. coli (the Nissle 1917) limits the expansion of the harmful strain of the bacteria. With further testing, the scientists believe they may be able to create a targeted antibiotic containing microcins that can halt or prevent the growth of dangerous bacteria in humans.

As a next step, the researchers are working to “purify” the microcins to assess the viability of targeted medication.