Escherichia coli (E. coli) is a group of gram-negative bacteria that normally reside in the intestine of healthy people, but some strains can cause infection.
People develop intestinal E. coli infections by eating contaminated food, touching infected animals, or swallowing contaminated water in a pool.
Intestinal infections can cause diarrhea, sometimes severe or bloody, and abdominal pain.
Antibiotics can effectively treat E. coli infections outside the digestive tract and most intestinal infections but are not used to treat intestinal infections by one strain of these bacteria.
Some strains of E. coli normally inhabit the digestive tract of healthy people. However, some strains of E. coli have acquired genes that enable them to cause infection in the digestive tract and in other parts of the body, most commonly the urinary tract. E. coli is the most common cause of bladder infection in women.
These bacteria can also cause infection of the prostate gland (prostatitis), gallbladder infection, infections that develop after appendicitis and diverticulitis, wound infections (including wounds made during surgery), infections in pressure sores, foot infections in people with diabetes, pneumonia, meningitis in newborns, and bloodstream infections. Many E. coli infections affecting areas outside the digestive tract develop in people who are debilitated, who are staying in a health care facility, or who have taken antibiotics.
These bacteria can also cause infections outside the intestine if the intestine is torn or damaged—for example, by an injury or a disorder, such as inflammatory bowel disease. Then, the bacteria may leave the intestine and spread to nearby structures that have no defenses against them or they may enter the bloodstream.
One strain produces a toxin that causes brief watery diarrhea. This disorder (called traveler’s diarrhea) usually occurs in travelers who consume contaminated food or water in areas where water is not adequately purified.