Which statement best describes Bacteroides fragilis?

• A. Is an aerobic gram-positive bacillus.
• B. Is an anaerobic gram-negative bacillus commonly associated with intra-abdominal infections.
• C. Is an obligate intracellular parasite.
• D. Is highly susceptible to all antibiotics.

Answer: (B)

The statement tests recognizing that Bacteroides fragilis is an anaerobic Gram-negative bacillus commonly associated with intra-abdominal infections. B. fragilis is a major member of the gut flora and thrives in low-oxygen environments, making it a frequent culprit in infections that involve the abdomen or peritoneal cavity when the intestinal barrier is breached. It often contributes to abscess formation and peritonitis. Additionally, it can produce beta-lactamase, giving it resistance to many penicillins, so it’s not susceptible to all antibiotics. It is not an aerobic organism, and it is not an obligate intracellular parasite, which helps distinguish it from other organisms described in the distractors.