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HelpTest Code MECPI Methicillin Resistance Gene, Molecular Detection, PCR, Varies
Infectious
Shipping Instructions
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.
Necessary Information
Organism identification and specimen source are required.
Specimen Required
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.
Useful For
Detecting mecA in staphylococcal bacterial isolates
Evaluating treatment options when oxacillin or cefoxitin breakpoints are unavailable (eg, certain Staphylococcus species other than Staphylococcus aureus)
Predicting antimicrobial resistance when bacterial growth is inadequate for phenotypic antimicrobial susceptibility testing (eg, staphylococcal small colony variants)
Assessing discrepancies amongst cefoxitin and oxacillin phenotypic testing results or penicillin-binding protein 2a test results
Special Instructions
Method Name
Real-Time Polymerase Chain Reaction (PCR)/Reverse Transcription PCR (RT-PCR)
Reporting Name
Methicillin Resistance Gene, VariesSpecimen Type
VariesSpecimen Minimum Volume
See Specimen Required
Specimen Stability Information
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Varies | Ambient (preferred) | ||
| Refrigerated | |||
Reject Due To
| Agar plate Mixed culture |
Reject |
Clinical Information
The presence of mecA has been associated with methicillin resistance in staphylococcal isolates. Rapid identification of mecA in staphylococcal isolates will help in determining which antimicrobial therapy to use when treating infections due to methicillin-resistant Staphylococcus aureus or methicillin-resistant Staphylococcus species other than S aureus.
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 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.
Testing of bacterial isolates by molecular methods may be needed when oxacillin or cefoxitin breakpoints are unavailable (eg, certain Staphylococcus species other than S aureus) or when discrepancies exist among cefoxitin and oxacillin phenotypic antimicrobial susceptibility testing results or PBP2a results. Use of this assay may also be helpful when isolates do not grow adequately for phenotypic antimicrobial susceptibility testing (eg, staphylococcal small colony variants).
Reference Values
Not detected
Interpretation
A positive result indicates the presence of the methicillin resistance gene (mecA) in the bacterial isolate.
A negative result indicates the absence of detectable DNA in the bacterial isolate.
Cautions
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.
This US Food and Drug Administration-modified assay will not predict methicillin resistance caused by mechanisms other than mecA. Methicillin resistance due to mecC is not assessed by this assay.
False-negative results may occur due to the presence of mecA in quantities lower than the limit of detection of the assay.
Mutations or polymorphisms in primer or probe binding regions may affect detection of new or unknown Staphylococcus aureus or methicillin-resistant S aureus variants resulting in a false-negative result.
Xpert SA Nasal Complete assay results may sometimes be invalid due to a failed sample processing control, an error, or lack of a result and may require retesting, which can lead to a delay in obtaining final results.
Supportive Data
Staphylococcal bacterial isolates were tested for the presence of mecA by the Cepheid GeneXpert - Xpert SA Nasal Complete compared to Mayo Clinic’s laboratory developed test (LDT) MARP / mecA, Molecular Detection, PCR, Varies. There was 95% or greater concordance for the detection of 25 mecA negative methicillin susceptible Staphylococcus species other than Staphylococcus aureus, 10 mecA negative methicillin susceptible S aureus, and 20 mecA positive methicillin-resistant S aureus. Greater than 95% concordance was achieved for 25 mecA positive methicillin-resistant Staphylococcus species other than S aureus isolates. Additionally, 10 isolates of Staphylococcus saccharolyticus and 10 isolates of small colony variant staphylococci were tested for the presence of mecA by both the Cepheid GeneXpert - Xpert SA Nasal Complete platform and the LDT, yielding 95% or greater correlation.
Method Description
The GeneXpert Dx System automates and integrates sample purification, nucleic acid amplification, and detection of the target sequence using real-time polymerase chain reaction (PCR). The system uses single-use disposable cartridges that hold the PCR reagents and host the PCR process. Because the cartridges are self-contained, cross-contamination is minimized. The test utilizes automated PCR for qualitative detection of proprietary sequences for the staphylococcal protein A (spa) gene, the gene for methicillin resistance (mecA), and the staphylococcal methicillin-resistant Staphylococcus aureus /S aureus DNA cassette chromosome mec (SCCmec) inserted into the S aureus chromosomal attB site. The assay includes a sample processing control to ensure the sample was processed correctly and to monitor for the presence of inhibitors in the PCR reaction. A probe check control verifies reagent rehydration, PCR tube filling in the cartridge, probe integrity, and dye stability.(Package insert: Xpert SA Nasal Complete 300-8799. Cepheid; Rev H, 09/2019)
Day(s) Performed
Monday through Friday
Report Available
2 to 4 daysSpecimen Retention Time
30 daysPerforming Laboratory
Mayo Clinic Laboratories in Rochester
Test Classification
This test has been modified from the manufacturer's instructions. Its performance characteristics were 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.CPT Code Information
87641
LOINC Code Information
| Test ID | Test Order Name | Order LOINC Value |
|---|---|---|
| MECPI | Methicillin Resistance Gene, Varies | 48813-0 |
| Result ID | Test Result Name | Result LOINC Value |
|---|---|---|
| MECPR | mecA Resistance Gene | 48813-0 |
| MEORG | Organism Identified by Client | In Process |
| MESCR | Specimen Source | 31208-2 |