Manuela Raffatellu, assistant professor of microbiology & molecular genetics, and colleagues at UC Irvine and the University of Washington identified how a probiotic strain of E. coli reduces salmonella colonization by competing with this pathogen for iron, an essential nutrient that salmonella acquires in the gut in order to replicate at high levels.

In fact, the researchers discovered that the E. coli strain called Nissle 1917 acquires iron more efficiently than does salmonella. As a result, salmonella counts in the gut decrease when Nissle is administered during infection. Study results appear in today's issue of Cell Host & Microbe.

"Although we focused on salmonella, our findings suggest that this approach can be effective against other gut bacterial pathogens that need iron to grow," said Raffatellu, who's also a member of UC Irvine's Institute for Immunology. "By understanding how these 'bad bugs' get nutrients, we can further study methods to eradicate them."

Most people infected with salmonella develop diarrhea, fever and abdominal cramps 24 to 72 hours after infection. The illness usually lasts four to seven days, and the majority of affected individuals recover without treatment. According to the Centers for Disease Control & Prevention, about 42,000 cases of salmonellosis are reported annually in the U.S. Because many milder cases are not diagnosed or reported, the actual number of infections is estimated to be between 1 million and 4 million per year.

For nearly a century, the E. coli Nissle 1917 strain has been administered to patients with a variety of bowel disorders, but little has been known about how this probiotic bacterium works. Nissle 1917 is a key ingredient in a German probiotic product currently unavailable in the U.S. market.

Elisa Deriu, Janet Liu, Milad Pezeshki, Robert Edwards, Roxanna Ochoa and Heidi Contreras of UC Irvine; and Stephen J. Libby and Ferric Fang of the University of Washington contributed to the study, which was funded by Public Health Service grants AI083663 and AI77629 and an Astellas Young Investigator Award from the Infectious Diseases Society of America Education & Research Foundation/National Foundation for Infectious Diseases. Work in the Raffatellu lab is also supported by UC Irvine's Pacific Southwest Regional Center of Excellence for Biodefense & Emerging Infectious Diseases (via award No. U54AI065359 from the National Institute of Allergy & Infectious Diseases).