3.22 Escherichia Coli (E. Coli)

Microbiology review for the USMLE Step 1 Exam

• Esherichia coli (E. coli) is a lactose-fermenting, gram-negative rod causing various diseases, ranging from mild gastroenteritis to septic shock.

• E. coli diseases can be divided into two categories: intestinal infections and extraintestinal infections (outside the GI system).

• E. coli is part of the normal flora in the human GI tract, but some strains are pathogenic.

• Four pathogenic strains of E. coli are Entertoxigenic E. coli (ETEC), Enterohemorrhagic E. coli (EHEC), Enteroinvasive E. coli (EIEC), and Enteropathogenic E. coli (EPEC).

• ETEC causes watery diarrhea and is commonly found in food and water in areas with inadequate sanitation and is the most important cause of travelers' diarrhea.

• EHEC, also called Shiga toxin-producing E. coli (STEC), causes bloody diarrhea and is associated with contaminated food (spinach, sprouts, lettuce, fruit, undercooked beef).

• Shiga toxin produced by EHEC causes cell death in the GI tract and can lead to hemolytic uremic syndrome (HUS) in about 10% of cases.

• EIEC causes dysentery-like symptoms such as abdominal pain, fever, and bloody diarrhea.

• EPEC causes diarrhea, malnutrition, and growth retardation, especially in children.

• Extraintestinal infections include urinary tract infections (UTIs), neonatal sepsis, and pneumonia (incomplete list)