Which of the following is an important virulence factor of Bacteroides fragilis?

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

Answer: (C)

The main concept here is that the polysaccharide capsule is the standout virulence factor for Bacteroides fragilis. This capsule forms a protective shield around the bacteria, making them resistant to phagocytosis by immune cells and less vulnerable to the complement system. That antiphagocytic barrier helps the organism survive in the host, particularly when it escapes from the gut into sterile sites, where it can form and sustain abscesses. While some strains may produce toxins such as enterotoxins or proteases that contribute to tissue damage, the capsule is the most consistently important feature driving virulence in B. fragilis. Neurotoxin isn’t associated with this organism, and exotoxins, though possible, aren’t the defining virulence factor here.