Detecting mecA in staphylococcal bacterial isolates
Evaluating treatment options when oxacillin or cefoxitin breakpoints are unavailable (eg, some Staphylococcus species, not Staphylococcus aureus)
Predicting antimicrobial resistance when bacterial growth is inadequate for phenotypic antimicrobial susceptibility testing (eg, staphylococcal small colony variants)
Assessing discrepancies between cefoxitin and oxacillin phenotypic testing results
This is a rapid molecular test that detects mecA DNA associated with prediction of antimicrobial resistance to methicillin and other applicable beta-lactam antibiotics in isolates of Staphylococcus species.
Real-Time Polymerase Chain Reaction (PCR) using LightCycler with Amplified Product Detection using Fluorescent Resonance Energy Transfer (FRET) Hybridization Probes
mecA
Staphylococcus
Staph
Varies
1. For shipping information see Infectious Specimen Shipping Guidelines .
2. Place specimen in a large infectious container and label as an etiologic agent/infectious substance.
Organism identification and specimen source are required.
Question ID | Description | Answers |
---|---|---|
MASRC | Specimen Source | |
MAORG | Organism Identified by Client |
Supplies: Infectious Container, Large (T146)
Container/Tube: Agar slant or other appropriate media
Specimen Volume: Organism in pure culture
Collection Instructions:
1. Perform isolation of bacteria.
2. Organism must be in pure culture, actively growing. Do not submit mixed cultures.
See Specimen Required
Agar plate Mixed culture | Reject |
Specimen Type | Temperature | Time | Special Container |
---|---|---|---|
Varies | Ambient (preferred) | ||
Frozen | |||
Refrigerated |
Detecting mecA in staphylococcal bacterial isolates
Evaluating treatment options when oxacillin or cefoxitin breakpoints are unavailable (eg, some Staphylococcus species, not Staphylococcus aureus)
Predicting antimicrobial resistance when bacterial growth is inadequate for phenotypic antimicrobial susceptibility testing (eg, staphylococcal small colony variants)
Assessing discrepancies between cefoxitin and oxacillin phenotypic testing results
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 can 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 Staphylococcus 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; SCV).
Not applicable
This polymerase chain reaction (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 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.
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 considering the patient's clinical condition.
False-negative results may occur due to inhibition of polymerase chain reaction, sequence variability underlying primers and probes, or the presence of the mecA genes in quantities lower than the limit of detection of the assay.
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.
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
Nucleic acids are released from bacterial isolates followed by polymerase chain reaction (PCR), which employs a target-specific detection system, including primers and fluorescent resonance energy transfer (FRET) hybridization probes that target the mecA gene. The LightCycler instrument amplifies and monitors target nucleic acid sequences by fluorescence during PCR cycling. This is an automated PCR system that rapidly detects amplified product development through stringent air-controlled temperature cycling and capillary cuvettes. Detection of amplified products is based on the FRET principle. For FRET product detection, a hybridization probe with a donor fluorophore, fluorescein, on the 3' end is excited by an external light source, which emits light that is absorbed by a second hybridization probe with an acceptor fluorophore. The acceptor fluorophore then emits light of a different wavelength that is measured with a signal proportional to the amount of specific PCR product. The detection process is completed in a closed system.(Cockerill FR, Uhl JR: Applications and challenges of real-time PCR for the clinical microbiology laboratory. In: Reischl U, Wittwer C, Cockerill F, eds. Rapid Cycle Real-Time PCR Methods and Applications. Springer-Verlag; 2002:3-27; Simner PJ, Humphries R: Special phenotypic methods for detecting antibacterial resistance: In: Carroll KC, Pfaller MA, eds. Manual of Clinical Microbiology. 12th ed. ASM Press; 2019:1316-1347)
Monday through Friday
This test was developed, and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the US Food and Drug Administration.
87150
Test Id | Test Order Name | Order LOINC Value |
---|---|---|
MARP | mecA PCR | 48813-0 |
Result Id | Test Result Name |
Result LOINC Value
Applies only to results expressed in units of measure originally reported by the performing laboratory. These values do not apply to results that are converted to other units of measure.
|
---|---|---|
MASRC | Specimen Source | 39111-0 |
MAORG | Organism Identified by Client | 43409-2 |
607725 | mecA PCR | 48813-0 |