Escherichia coli are the most numerous aerobic commensal inhabitants of the large intestine. Certain strains cause diarrhea, and all can cause infection when they invade sterile sites (eg, the urinary tract). Diagnosis is by standard culture techniques. Toxin assays may help identify the cause of diarrhea. Treatment with antibiotics is guided by susceptibility testing.
Most commonly, E. coli cause UTIs, which usually represent ascending infection (ie, from the perineum via the urethra).
E. coli normally inhabit the GI tract; however, some strains have acquired genes that enable them to cause intestinal infection. When ingested, the following strains can cause diarrhea:
Other strains are capable of causing extraintestinal infection if normal intestinal anatomic barriers are disrupted (eg, by ischemia, inflammatory bowel disease, or trauma), in which case the organism may spread to adjacent structures or invade the bloodstream. Hepatobiliary, peritoneal, cutaneous, and pulmonary infections also occur. E. coli bacteremia may also occur without an evident portal of entry.
In neonates, particularly preterm infants, E. coli bacteremia and meningitis (caused by strains with the K1 capsule, a marker for neuroinvasiveness) are common (see discussed in Neonatal Bacterial Meningitis and discussed in Neonatal Sepsis).
Samples of blood, stool, or other clinical material are sent for culture. If an enterohemorrhagic strain is suspected, the laboratory must be notified because special culture media are required.
Treatment must be started empirically based on the site and severity of infection (eg, mild bladder infection, urosepsis) and then modified based on antibiotic susceptibility testing. Many strains are resistant to ampicillin and tetracyclines, so other drugs should be used; they include ticarcillin, piperacillin, cephalosporins, aminoglycosides, trimethoprim/sulfamethoxazole (TMP/SMX), and fluoroquinolones.
Surgery may be required to drain pus, debride necrotic lesions, or remove foreign bodies.
Besides being resistant to ampicillin and tetracycline, E. coli have become increasingly resistant to TMP/SMX and fluoroquinolones. Also, multidrug-resistant strains that produce extended-spectrum β-lactamases (ESBLs) have emerged as an important cause of community-acquired UTI and sepsis. ESBLs can hydrolyze most β-lactams, including penicillins and broad-spectrum cephalosporins and monobactams, but not carbapenems (imipenem, meropenem, doripenem, ertapenem); carbapenems should be used for ESBL-producing E. coli.
Last full review/revision February 2014 by Larry M. Bush, MD; Maria T. Perez, MD
Content last modified March 2014