Merck Manual

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Escherichia coli Infections

(E. coli)

By

Larry M. Bush

, MD, FACP, Charles E. Schmidt College of Medicine, Florida Atlantic University;


Maria T. Vazquez-Pertejo

, MD, FACP, Wellington Regional Medical Center

Last full review/revision Apr 2022| Content last modified Apr 2022
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The gram-negative bacterium Escherichia coli is the most numerous aerobic commensal inhabitant 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. Antibiotics are not indicated for enterohemorrhagic E. coli infections.

Diseases caused by E. coli

  • Urinary tract infection (UTI; most common)

  • Enteric infection (certain strains)

  • Invasive infection (rare, except in neonates)

  • Infection at other sites

Most commonly, E. coli cause UTIs, which usually represent ascending infection (ie, from the perineum via the urethra). E. coli may also cause prostatitis and pelvic inflammatory disease (PID).

E. coli normally inhabit the gastrointestinal 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, colonic diverticulitis, 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.

Diagnosis of E. coli Infections

  • Culture

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 of E. coli Infections

  • Various antibiotics depending on site of infection and susceptibility testing

Treatment of E. coli infections 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 piperacillin, cephalosporins, carbapenems, fosfomycin, nitrofurantoin, aminoglycosides, trimethoprim/sulfamethoxazole (TMP/SMX), and fluoroquinolones.

Surgery may be required to control the source of infection (eg, to drain pus, debride necrotic lesions, or remove foreign bodies).

Drug resistance

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 beta-lactamases (ESBLs) have emerged as an important cause of community-acquired UTI and sepsis. ESBLs can hydrolyze most beta-lactams, including penicillins and broad-spectrum cephalosporins and monobactams but not carbapenems (imipenem, meropenem, doripenem, ertapenem); carbapenems and newer beta-lactam/beta-lactamase inhibitor combination drugs should be used for ESBL-producing E. coli.

E. coli have also acquired resistance genes that encode AmpC beta-lactamases, serine carbapenemases, and metallo-carbapenemases. The tetracycline–like agents (eg, tigecycline, eravacycline) and cefiderocol (an injectable siderophore cephalosporin) are also active against ESBL-producing strains as well as AmpC beta-lactamase–, serine carbapenemase–, and metallo-carbapenemase–producing strains. Fosfomycin has activity against multidrug-resistant strains and is an oral alternative for lower UTIs.

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NOTE: This is the Professional Version. CONSUMERS: Click here for the Consumer Version
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