Which antibiotic combination is well known to be effective against MRSA?

• A. Keflex
• B. Bacitracin
• C. Bactrim (Sulfamethoxazole + Trimethoprim)
• D. Dicloxacillin

Answer: (C)

MRSA resists many antibiotics in the beta-lactam family because it carries a mecA gene that alters the penicillin-binding protein, reducing the effectiveness of drugs like cephalexin and dicloxacillin. Because of that, treatments that work through different mechanisms are favored. Sulfamethoxazole-trimethoprim blocks two sequential steps in bacterial folate synthesis, giving reliable activity against MRSA and making it a well-established option for MRSA-related skin and soft tissue infections. This mechanism is separate from beta-lactams, so MRSA is typically susceptible to this combination, unlike the beta-lactam antibiotics listed. Bacitracin is mainly used topically and isn’t consistently effective against MRSA systemically, and the beta-lactams shown are not reliable for MRSA due to resistance.