Mutation-Based Antibiotic Resistance Mechanism in Methicillin-Resistant Staphylococcus aureus Clinical Isolates

Area of Science:

• Microbiology
• Molecular Biology
• Drug Resistance

Background:

• β-Lactam antibiotics are essential for treating bacterial infections by inhibiting peptidoglycan synthesis.
• Staphylococcus aureus develops resistance through penicillin-binding protein 2a (PBP2a), encoded by mecA, which has low affinity for these antibiotics.

Purpose of the Study:

• To investigate the diversity and functional role of missense mutations in PBP2a contributing to antibiotic resistance.
• To analyze sequence variations in the mecA gene of clinical MRSA isolates.

Main Methods:

• Phenotypic and genotypic identification of methicillin-resistant Staphylococcus aureus (MRSA) from clinical samples.
• Sequence variation analysis of the mecA gene.
• Protein-ligand docking to assess the impact of mutations on PBP2a-cefoxitin interaction.

Main Results:

• MRSA was most frequent in wound specimens (60%).
• Four amino acid substitutions in PBP2a were identified: E239K, E239R, G246E, and E447K.
• A novel E239R mutation in the allosteric site altered PBP2a's active site conformation, hindering cefoxitin binding and conferring high-level resistance.

Conclusions:

• Missense mutations in PBP2a, particularly E239R, significantly contribute to cefoxitin resistance in MRSA.
• Allosteric site mutations can induce conformational changes, leading to reduced antibiotic susceptibility.
• Understanding these mutations is crucial for developing strategies against MRSA infections.