mecA / mecC — Methicillin resistance (MRSA, MRSE)

Mechanism

Encodes PBP2a, an altered penicillin-binding protein with low affinity for most beta-lactams.

What it removes from the grid

Oxacillin, nafcillin, dicloxacillin, cefazolin, cephalexin, amoxicillin-clavulanate, ampicillin-sulbactam and most other beta-lactams for the staphylococci.

What it spares

Ceftaroline, the anti-MRSA cephalosporin built to bind PBP2a. Non-beta-lactam agents are unaffected by this gene.

A multiplex panel can't say which organism in a mixed specimen carries a detected gene. CORE-ABR applies mecA / mecC only to organisms known to carry it, and only to the agents its mechanism defeats — so a detected gene moves the right cells and spares the rest.

Organisms it is applied to

Staphylococcus aureusThe leading cause of skin and soft-tissue infection, and the organism most wound reports are built around.Gram-positive bacteria · UTI · Wound · STI Staphylococcus epidermidisA coagulase-negative staphylococcus that lives on normal skin. Usually a colonizer; sometimes the cause — particularly w…Gram-positive bacteria · UTI · Wound

Coding

MRSA infections are coded with combination codes (for example B95.62, or A49.02 for unspecified-site MRSA infection). Per ICD-10-CM guidelines, Z16.11 is not added alongside an MRSA combination code. CORE-ABR adds resistance findings as supporting codes, not primary, and prints the rationale on the report.

Tagged

Decision support only. The treating clinician decides. Molecular genotype does not replace phenotypic susceptibility testing, culture, or public-health reporting. Absence of a detected resistance gene does not establish susceptibility. Organism targets vary by panel; CORE-ABR is configured to the assay each laboratory runs.