From the Research
The primary gene responsible for MRSA resistance is mecA, which encodes for an altered penicillin-binding protein called PBP2a, allowing cell wall synthesis to continue even in the presence of beta-lactam antibiotics. This gene is carried on a mobile genetic element called the Staphylococcal Cassette Chromosome mec (SCCmec), which can be transferred between bacteria 1. The mecA gene provides a broad selective advantage across diverse chemical environments, including beta-lactam and non-beta-lactam antibiotics, non-antibiotic drugs, and natural and synthetic compounds 1.
Key Points
- The mecA gene is the primary determinant of MRSA resistance to beta-lactam antibiotics 2, 3.
- The mecA gene encodes for an altered penicillin-binding protein called PBP2a, which has a lower affinity for beta-lactam antibiotics 2, 3.
- The mecA gene is carried on a mobile genetic element called the Staphylococcal Cassette Chromosome mec (SCCmec), which can be transferred between bacteria 1, 3.
- MRSA strains often carry other resistance genes that confer protection against multiple antibiotic classes, making these infections particularly challenging to treat 2, 3.
Mechanism of Resistance
The mecA gene is regulated by a complex system involving a sensor-inducer (MecR1) and a repressor (MecI), as well as an anti-repressor (MecR2) that promotes the proteolysis of the mecA repressor and enables optimal expression of beta-lactam resistance in MRSA 4, 5. The mecA gene provides a widespread advantage across beta-lactam and non-beta-lactam antibiotics, non-antibiotic drugs, and diverse natural and synthetic compounds, depending on the presence of subinhibitory levels of the beta-lactam drug cefoxitin 1.
Clinical Implications
Understanding the mecA resistance mechanism is crucial for developing new antimicrobial strategies and implementing effective infection control measures to prevent MRSA spread 2, 3. Treatment of MRSA infections typically requires alternative antibiotics such as vancomycin, linezolid, daptomycin, or trimethoprim-sulfamethoxazole, depending on the specific strain's susceptibility pattern and the site of infection 2, 3.