Haemophilus influenzae strains that produce beta-lactamase are resistant to which antibiotic?

Haemophilus influenzae strains that produce beta-lactamase are resistant to which antibiotic?

• A. Chloramphenicol
• B. Erythromycin
• C. Ampicillin
• D. Trimethoprim-Sulfamethoxazole

Answer: (C)

Beta-lactamase production in Haemophilus influenzae breaks open the beta-lactam ring that defines penicillin-class antibiotics. Ampicillin is a beta-lactam antibiotic, so strains that produce beta-lactamase can hydrolyze ampicillin and become resistant to it. The other drugs listed are not beta-lactams, so their activity isn’t directly neutralized by beta-lactamase—chloramphenicol and erythromycin inhibit protein synthesis, and trimethoprim-sulfamethoxazole blocks folate synthesis. Therefore, the antibiotic these beta-lactamase–producing strains resist is ampicillin.

Beta-lactamase production in Haemophilus influenzae breaks open the beta-lactam ring that defines penicillin-class antibiotics. Ampicillin is a beta-lactam antibiotic, so strains that produce beta-lactamase can hydrolyze ampicillin and become resistant to it. The other drugs listed are not beta-lactams, so their activity isn’t directly neutralized by beta-lactamase—chloramphenicol and erythromycin inhibit protein synthesis, and trimethoprim-sulfamethoxazole blocks folate synthesis. Therefore, the antibiotic these beta-lactamase–producing strains resist is ampicillin.