• Sorbitol and lactose fermenters (except for EHEC, which does not ferment sorbitol)
• Form pink colonies on MacConkey agar
• Form green colonies with a metallic sheen on eosin-methylene blue agar
• Present the enterobacterial common antigen (ECA) on their surface
• Produce beta-galactosidase (cleaves lactose into galactose and glucose)
• Common virulence factors
  • Lipopolysaccharide (LPS)
    • Activates macrophages → widespread release of IL-1, IL-6 & TNF-α
    • Bacteremia & septic shock
  • K1 capsular polysaccharide
    • Prevents phagocytosis & complement-mediated lysis
    • Neonatal meningitis
  • Shiga toxin
    • Inactivates 60S ribosomal subunit, halting protein synthesis & causing cell death
    • Gastroenteritis (bloody)
  • Heat-stable/heat-labile enterotoxins
    • Promotes fluid & electrolyte secretion from intestinal epithelium
    • Gastroenteritis (watery)
  • P-fimbriae
    • Allows adhesion to uroepithelium
    • Urinary tract infection