Test Catalog

Test ID: MARP    
mecA, Molecular Detection, PCR, Varies

Useful For Suggests clinical disorders or settings where the test may be helpful

Detection of mecA in staphylococcal bacterial isolates


Evaluation of treatment options when oxacillin or cefoxitin breakpoints are unavailable (eg, some Staphylococcus species, not S aureus)


Prediction of antimicrobial resistance when bacterial growth is inadequate for phenotypic antimicrobial susceptibility testing (eg, staphylococcal small colony variants; SCVs)


Assessment of discrepancies between cefoxitin and oxacillin phenotypic testing results

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Bacteria can acquire resistance to certain beta-lactam antibiotics through a variety of mechanisms. One such mechanism is the mecA gene. The mecA gene encodes penicillin-binding protein 2a (PBP2a), which is a PBP that has a low affinity for beta-lactam antibiotics. Bacteria expressing this gene are able to maintain cell wall synthesis even in the presence of beta-lactam antibiotics. Clinically significant mecA-mediated resistance is restricted to staphylococci.


Testing of bacterial isolates by molecular methods may be needed when oxacillin or cefoxitin breakpoints are unavailable (eg, Staphylococcus species, not S aureus) or when discrepancies between cefoxitin and oxacillin phenotypic antimicrobial susceptibility testing results exist. Use of this assay may also be helpful when isolates do not grow adequately for phenotypic antimicrobial susceptibility testing (eg, staphylococcal small colony variants; SCVs).

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

Not applicable

Interpretation Provides information to assist in interpretation of the test results

This PCR detects the mecA gene. A positive result for this mecA PCR test strongly suggests resistance to beta-lactam antibiotics other than ceftaroline in a staphylococcal isolate. If the mecA PCR test is positive, and the patient is on a beta-lactam antimicrobial that would be predicted to be resistant, the clinician should consider escalating the antimicrobial treatment to an appropriate therapy.


A negative result indicates the absence of detectable DNA.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

Only pure isolates of staphylococcal species should be tested.


This test should be used in conjunction with phenotypic antimicrobial susceptibility tests, when available, and interpreted in light of the patient's clinical condition.


False-negative results may occur due to inhibition of PCR, sequence variability underlying primers and probes, or the presence of the mecA genes in quantities lower than the limit of detection of the assay.

Supportive Data

This test demonstrated 100% concordance for testing performed on 72 methicillin-resistant Staphylococcus aureus (MRSA) isolates and 42 methicillin-susceptible S aureus (MSSA) isolates.


In addition, this test demonstrated 100% concordance for 43 methicillin-resistant Staphylococcus isolates, not S aureus, and 96.5% concordance for 57 methicillin-susceptible Staphylococcus isolates, not S aureus.

Clinical Reference Recommendations for in-depth reading of a clinical nature

Miragaia M. Factors Contributing to the Evolution of mecA-Mediated Beta-lactam Resistance in Staphylococci: Update and New Insights From Whole Genome Sequencing (WGS). Front Microbiol. 2018 Nov 13;9:2723. doi: 10.3389/fmicb.2018.02723

Special Instructions Library of PDFs including pertinent information and forms related to the test