Microbiology · Enterobacterales
Escherichia coli !
- Bacterium
- Gram-negative
- Contact
- Exam priority: high
A normal gut bacterium. Some strains cause most urinary infections, plus diarrhea, newborn meningitis and sepsis.
Updated 2026-11-01
Also called: E. coli
At a glance
- Gram
- Gram-negative
- Shape
- Rod
- Oxygen
- Facultative anaerobe
- Family
- Enterobacteriaceae
- Stain
- Gram: red rods
Morphology
- Motile Gram-negative rod with flagella
- Lactose fermenter: pink colonies on MacConkey and a green metallic sheen on EMB agar
- Indole-positive, oxidase-negative
- E. coli O157:H7 does not ferment sorbitol (colorless colonies on sorbitol-MacConkey)
Transmission
- Urinary infection: the person's own gut flora climbs from the perineum up the urethra
- Diarrhea: water or food contaminated with feces; undercooked ground beef, raw milk and raw produce (EHEC)
- Newborn: from maternal vaginal flora during birth
- Contact (on top of standard) for diapered or incontinent patients with diarrhea
Reservoir: Human and animal gut; Cattle: main reservoir of E. coli O157:H7
Isolation precautions
What the care team adds to standard precautions.
- Contact
- Gown and gloves; dedicated equipment. For C. difficile, soap-and-water hand washing.
Virulence factors
- P fimbriae: attachment to upper urothelium, pyelonephritis
- Type 1 fimbriae: bladder attachment, cystitis
- K1 capsule: neonatal meningitis
- ETEC: heat-labile toxin (raises cAMP) and heat-stable toxin (raises cGMP), watery traveler's diarrhea
- EHEC: Shiga toxin stops protein synthesis (60S subunit), injures endothelium and causes hemolytic uremic syndrome
- EIEC invades the mucosa (dysentery); EPEC attaches and effaces microvilli (infant diarrhea)
- LPS: fever and septic shock
Diseases it causes
- Lower urinary tract infection (cystitis): the leading cause Urinary tract infection (acute cystitis) →
- Acute pyelonephritis Acute pyelonephritis →
- Hemolytic uremic syndrome after bloody diarrhea from EHEC Hemolytic uremic syndrome (HUS) →
- Neonatal sepsis Neonatal sepsis →
- Neonatal meningitis from K1 strains Bacterial meningitis →
- Acute gastroenteritis and traveler's diarrhea (ETEC) Acute (viral) gastroenteritis →
Clinical picture
- Dysuria, urgency and frequency; fever and flank pain if it reaches the kidney
- Bloody diarrhea without high fever: think EHEC
- Hemolytic anemia, low platelets and acute kidney injury a week later: hemolytic uremic syndrome
Diagnosis
- Urinalysis: positive nitrite and leukocyte esterase; urine culture with colony count
- Stool culture on sorbitol-MacConkey and detection of Shiga toxin or its genes by PCR
- Blood and CSF culture in newborns
- Susceptibility testing: look for extended-spectrum beta-lactamases (ESBL)
Treatment
Lower urinary infection: nitrofurantoin or fosfomycin depending on local resistance; pyelonephritis and sepsis: third-generation cephalosporins or other beta-lactams; ESBL strains: carbapenems. Antibiotics are not used in EHEC diarrhea because they can raise the risk of hemolytic uremic syndrome.
Drug class only; doses and regimens are set by the clinician from the current guideline.
In Pharmacology:
Prevention
- Cook ground beef through and use pasteurized milk
- Handwashing and keeping raw and cooked food apart
- Safe water
- Early removal of urinary catheters
Test yourself
Think of the answer, then tap the question to see it.
Which bacterium causes most urinary tract infections?
Uropathogenic Escherichia coli.
Why are antibiotics withheld in bloody diarrhea from E. coli O157:H7?
They can increase Shiga toxin release and the risk of hemolytic uremic syndrome.
Which medium separates E. coli O157:H7 from other strains?
Sorbitol-MacConkey agar: O157:H7 does not ferment sorbitol and gives colorless colonies.
Which E. coli virulence factor is linked to neonatal meningitis?
The K1 capsule.
How do the LT and ST toxins of enterotoxigenic E. coli work?
LT raises cAMP and ST raises cGMP in the enterocyte; both drive water secretion and watery diarrhea.
Related
Related conditions
- Urinary tract infection (acute cystitis)
- Acute pyelonephritis
- Hemolytic uremic syndrome (HUS)
- Neonatal sepsis
- Bacterial meningitis
- Acute (viral) gastroenteritis
← Back to the group: Enterobacterales
Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.
Sources: Escherichia coli Infections (MSD Manual Professional Edition, 2026); E. coli (WHO, 2018); Urinary Tract Infections (MedlinePlus, 2025).
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Representative model, for educational purposes only.