Escherichia coli Overview 

• Characteristics
  • Gram negative rod
    • motile
  • Indole +
  • Lactose-fermenting
    • Grows on eosin methylene blue (EMB) agar, where lactose fermentation produces a blue-green color
    • Can also ferment glucose
  • Facultative anaerobic
• Presentation
  • Over 100 strains cause disease
    • Each strain has different virulence factors, which determines disease
  • UTI
    • most common cause of UTI (>80%)
    • Mediated by pili/fimbriae
      • enable adhesion to uroepithelial surface
    • May present as cystitis, urethritis, or pyelonephritis
  • Diarrhea
    • ETEC causes watery diarrhea
    • EHEC causes bloody diarrhea
      • enteroinvasive E. coli (EIEC) strains are rare cause
  • Neonatal Meningitis
    • Mediated by K1 capsule
    • Prevents phagocytosis or complement activation
  • Sepsis
    • Most common cause of gram-negative sepsis
    • Mediated by LPS endotoxin
      • seen in all gram-negative bacteria
  • May be causative agent in a variety of other infections
    • osteomyelitis in sickle cell patients
    • intra-abdominal and lung abscesses
    • orchitis in older men
• Treatment
  • Generally supportive, as antibiotics are rarely indicated