Practice question from Pathology & Microbiology
A patient with a dental abscess is found to have an infection with bacteria that only grow in an anaerobic chamber. Blood agar plates show no growth after 48 hours of aerobic incubation. Which enzyme deficiency BEST explains why these organisms cannot survive in the presence of oxygen? A. Transpeptidase B. β-lactamase C. Catalase and superoxide dismutase D. DNA gyrase E. Peptidoglycan synthase
Answer
C
Explanation
Obligate anaerobes lack catalase (which breaks down H₂O₂) and superoxide dismutase (which converts superoxide radicals to H₂O₂). When exposed to oxygen, toxic reactive oxygen species (superoxide, hydrogen peroxide, hydroxyl radicals) accumulate and cause lethal oxidative damage to DNA, proteins, and lipids. Dental abscesses commonly contain obligate anaerobes like Bacteroides, Prevotella, Fusobacterium, and Peptostreptococcus. Clinically, anaerobic infections often have a foul odor and require specific antibiotics (metronidazole, clindamycin, or β-lactam/β-lactamase inhibitor combinations). Options A, D, and E are enzymes present in most bacteria. Option B (β-lactamase) is an antibiotic resistance enzyme unrelated to oxygen tolerance.