What Are the Various Manifestations of E. coli Infection of the Colon and How Should It Be Treated?
Escherichia coli (E. coli) is a common commensal organism of the gastrointestinal tract. However, when specific additional genes are acquired by these bacteria, they may become pathogenic, and E. coli represents one of the most common bacterial causes of diarrheal illness in humans. There are 5 specific forms of E. coli that are clinically relevant: enterotoxigenic E. coli (ETEC), enteropathogenic E. coli (EPEC), enterohemorrhagic E. coli (EHEC), enteroinvasive E. coli (EIEC), and enteroaggregative E. coli (EAEC). The pathogenic E. coli cannot be distinguished from nonpathogenic strains by culture or routine biochemical testing, and additional testing must be performed. Currently, EHEC O157 is the only pathogenic strain readily identified in the clinical laboratory; further testing is currently only performed in research laboratories.1,2
ETEC has emerged as a significant pathogen in the United States and elsewhere. It is a fastidious organism and is commonly found in food and water supplies, particularly in developing nations. It is one of the most common bacterial causes of diarrheal illness in children younger than 2 years of age and is the most frequent cause of “traveler’s diarrhea.” After exposure, the patient usually experiences watery diarrhea, which may be very similar to cholera with some nausea. Vomiting is uncommon. Usually the illness lasts less than 24 hours, but can persist for up to 4 or 5 days. Currently, the diagnosis is only performed in research laboratories. Treatment consists primarily of oral rehydration. In most cases, the disease is self-limited, and antimicrobial therapy is usually not necessary. If treatment is necessary, consideration may be given for ciprofloxacin or a nonabsorbed gut-specific antibiotic, such as rifaximin.
EPEC primarily causes diarrhea in children, particularly neonates, and is an uncommon cause of clinical symptoms in adults. The diarrheal illness induced by EPEC can be extremely severe with vomiting and associated dehydration and malnutrition. Current means of diagnosis requires a deoxyribonucleic acid probe or polymerase chain reaction of the EPEC adherence factor and is performed only in research laboratories. Therapy consists of supportive care with rehydration.
As its name would imply, EHEC has been associated with outbreaks of bloody diarrhea. The production of one or more pathogenic Shiga toxins (of which O157:H7 is the most prevalent) by EHEC differentiates this organism from other E. coli species and is associated with an increased incidence of serious complications. Although infected beef is the most likely vector, ingestion of contaminated milk, drinking water, fruits, and vegetables has been isolated as a source of epidemics with EHEC. Once exposed, the incubation period is between 3 and 4 days. In addition to causing colitis, EHEC is also associated with hemolytic-uremic syndrome (HUS), primarily in children under age 10 and the elderly. HUS is characterized by the triad of acute renal failure, microangiopathic hemolytic anemia, and thrombocytopenia. EHEC should be considered in any patient who presents with bloody diarrhea, particularly in the setting of prominent abdominal pain without fever.3 Diagnosis is made by stool culture with specific testing for O157:H7 on sorbitol-MacConkey agar. Sorbitol negative colonies that are confirmed as E. coli are subsequently tested to see if they react with antiserum to O157 antigen. The only treatment of EHEC is supportive care with monitoring for the complications of HUS. Antibiotic therapy is not recommended due to the risk of increased production or release of toxin. In patients with HUS, consideration may be given for other therapies including plasma exchange, plasma infusion, or intravenous immunoglobulin, although these are of uncertain benefit.
EIEC causes a diarrhea that is very similar to shigellosis—watery and often associated with fever and abdominal cramping. The diarrhea associated with EIEC may occasionally be bloody. With an incubation period of less than 24 hours, EIEC contains adherence factors that allow it to invade enterocytes where it can multiply and move to adjacent intestinal cells. A definitive diagnosis can be made by stool culture with DNA probe searching for EIEC. Treatment is usually supportive with the goal of rehydration. In advanced cases, antimicrobial therapy with trimethoprim-sulfamethoxazole may be utilized.
EAEC causes persistent watery diarrhea usually in children, primarily in developing countries, though outbreaks have been reported in Europe and cases have been reported in HIV-infected adults. The complete pathogenesis of EAEC is not completely understood. Diagnosis is made by identification of a tissue adherence factor and is only performed in research laboratories. Successful treatment and eradication can be achieved via treatment with ciprofloxacin.
1. Nataro JP, Kaper JB. Diarrheagenic Escherichia coli. Clin Microbiol Rev. 1998;11(1):142-201.
2. March SB, Ratnam S. Sorbitol-MacConkey medium for detection of Escherichia coli O157:H7 associated with hemorrhagic colitis. J Clin Microbiol. 1986;23(5):869-872.
3. Boyce TG, Swerdlow DL, Griffin PM. Escherichia coli O157:H7 and the hemolytic-uremic syndrome. N Engl J Med. 1995;333(6):364-368.