Explain how Staphylococcus aureus becomes resistant to penicillin by altering its penicillin‑binding proteins (PBPs).
Answer
Resistance arises because the bacterium acquires mutated PBPs with reduced affinity for penicillin, preventing inhibition of cell‑wall synthesis.
Step-by-step solution
- State that penicillin normally binds to PBPs, inhibiting transpeptidation in peptidoglycan synthesis.
- Explain that genetic mutations or acquisition of mecA gene can produce altered PBPs (PBP2a).
- Describe how the altered PBPs have low binding affinity for β‑lactam antibiotics, so cell‑wall synthesis continues.
- Conclude that this structural change confers resistance to penicillin.
Common mistake: Attributing resistance only to β‑lactamase production
Concept tested: Antibiotic resistance via target modification
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