Which statement about the Bacteroides fragilis group is true?

• A. They are inhibited by bile
• B. They are non-gram-negative
• C. They are spore-forming
• D. They are resistant to penicillin

Answer: (D)

Penicillin resistance in Bacteroides fragilis group stems from their ability to produce beta-lactamase, an enzyme that breaks down penicillin and related drugs. This makes these organisms notoriously resistant to penicillin, so that statement is true and clinically important because it guides treatment toward beta-lactamase inhibitors or non-penicillin antibiotics. These bacteria are Gram-negative, anaerobic rods that are non-spore-forming, and they tolerate bile (in fact, they can grow in bile-containing media), so the ideas that they are inhibited by bile or that they form spores do not fit. Understanding this resistance pattern explains why penicillin alone is often ineffective against these organisms.