mecA gene

The mecA gene is a genetic element that encodes for a penicillin-binding protein (PBP2a) in bacteria, particularly in Staphylococcus aureus. This gene is responsible for conferring resistance to beta-lactam antibiotics, including methicillin, oxacillin, and other penicillinase-resistant penicillins.

Mechanism of Resistance:

• The mecA gene produces a modified penicillin-binding protein (PBP2a) with a low affinity for beta-lactam antibiotics.
• Normally, beta-lactam antibiotics work by binding to penicillin-binding proteins (PBPs) on the bacterial cell wall, inhibiting cell wall synthesis and leading to bacterial cell death.
• However, the altered PBP2a produced by the mecA gene has a reduced affinity for beta-lactam antibiotics, allowing the bacteria to continue synthesizing their cell wall despite the presence of the antibiotic.

Clinical Significance:

• Methicillin-resistant Staphylococcus aureus (MRSA) strains carry the mecA gene, making them resistant to methicillin and other beta-lactam antibiotics.
• MRSA infections are associated with increased morbidity and mortality rates compared to infections caused by methicillin-sensitive Staphylococcus aureus (MSSA).
• Treatment of MRSA infections often requires alternative antibiotics, such as vancomycin, linezolid, daptomycin, or newer agents like ceftaroline.

Detection of mecA Gene:

• The mecA gene can be detected using molecular techniques such as polymerase chain reaction (PCR) or real-time PCR.
• PCR assays targeting the mecA gene are commonly used in clinical microbiology laboratories to identify MRSA strains rapidly.

Evolution and Spread:

• The mecA gene is located on a mobile genetic element called the staphylococcal chromosomal cassette (SCC), which can be transferred between bacteria via horizontal gene transfer.
• The widespread use of antibiotics, especially beta-lactams, has contributed to the selection and dissemination of MRSA strains carrying the mecA gene.
• Some strains of Staphylococcus aureus have acquired additional resistance mechanisms, leading to multidrug-resistant (MDR) or extensively drug-resistant (XDR) phenotypes.

Overall, the mecA gene plays a crucial role in the development of antibiotic resistance in Staphylococcus aureus and has significant implications for the treatment and control of MRSA infections in healthcare settings and the community.

References:
1. Wielders, C. L. C., Fluit, A. C., Brisse, S., Verhoef, J., & Schmitz, F. J. (2002). mecA Gene Is Widely Disseminated in Staphylococcus aureus Population. 40(11), 3970–3975. https://doi.org/10.1128/JCM.40.11.3970

 2. Ito, T., and K. Hiramatsu. 1998. Acquisition of methicillin resistance and

progression of multiantibiotic resistance in methicillin-resistant Staphylococcus

aureus. Yonsei Med. J. 39:526–533.

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