A non-healing leg infection after antibiotics raises suspicion for which organism?

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When a leg infection doesn’t improve with standard antibiotics, consider an organism that’s resistant to many common drugs. Methicillin-resistant Staphylococcus aureus (MRSA) is a classic culprit in this scenario. MRSA carries the mecA gene, producing a penicillin-binding protein (PBP2a) with low affinity for beta-lactam antibiotics, so drugs like methicillin and most penicillins or cephalosporins fail to clear the infection. In practice, MRSA often presents as skin or soft tissue infections that persist or worsen despite usual therapy, including boils or cellulitis. Ring worm, on the other hand, is fungal and would not respond to antibiotics at all, which makes it less likely in this antibiotic-failure context. Folliculitis and boils can be caused by Staph aureus, but when they don’t heal with typical antibiotics, MRSA is the concern.