Bacterial pathogenesis

Question 1

How do bacteria adhere to epithelial cells?

Answer 1

Occurs via surface proteins:
• fimbriae (occurs in many gram -ve bacteria)
E.g. K88 in pigs for ETEC
• non-fimbriate adhesins

Question 2

How do bacteria enter/invade host cells?

Answer 2

Penetrate epithelium:
• Through cells
• Between cells
• Often via pathogen-mediated endocytosis
• Initiated by bacterial surface proteins via invasins
E.g. Yersinia

Question 3

How do bacteria directly evade phagocytosis?

Answer 3

• Production of leukocidins, enzymes that kill WBCs, e.g. S. pyrogenes
• Production of anti-inflammatory toxins and enzymes
• Carriage of surface anti-phagocytic structures (capsule)

Question 4

How do bacteria evade phagocytosis?

Answer 4

1. Direct evasion of phagocytosis
2. Interfering with opsonins:
   - Antibodies e.g. produce IgA protease
   - Complement