Which virulence factor is important for Bacteroides fragilis?

• A. Endotoxin
• B. Exotoxins
• C. Polysaccharide capsule
• D. Protease

Answer: (C)

The key factor driving the virulence of Bacteroides fragilis is its polysaccharide capsule. This capsule coats the bacterial surface and makes the organism highly resistant to immune clearance, especially phagocytosis and complement-mediated killing. That ability to evade the host’s frontline defenses allows B. fragilis to persist in tissues and promote the formation of anaerobic abscesses, particularly when mucosal barriers are breached.

Other potential factors like proteases or endotoxins can contribute to inflammation or tissue damage, but they don’t shape the organism’s disease-causing potential as prominently as the capsule does. Exotoxins are not the hallmark virulence feature for this bacterium, and while endotoxin (LPS) exists, the capsule’s role in immune evasion and abscess formation is the defining factor.