A study suggests that a harmless strain of Escherichia coli called Nissle 1917 primes the small intestine to defend itself against another strain that causes potentially fatal infections.
Most strains of the bacterium E. coli are benign, but some can cause severe illness, including stomach cramps, vomiting, and diarrhea. The bacteria can spread via contaminated food and water or through contact with an animal or person who has the infection.
Other strains can cause urinary tract infections, respiratory illness, and pneumonia.
Some of the most dangerous E. coli strains produce a toxin called Shiga. In the United States, the Centers for Disease Control and Prevention (CDC) estimate that these strains are responsible for 265,000 infections annually.