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Updated: Apr 25, 2026
Multiplex PCR Assay for Typing of Staphylococcal Cassette Chromosome Mec Types I to V in Methicillin-resistant Staphylococcus aureus
Published on: September 5, 2013
Identification of agr-positive methicillin-resistant Staphylococcus aureus harbouring the class A mec complex by
Michaele Josten1, Jasmin Dischinger1, Christiane Szekat1
1Institute of Medical Microbiology, Immunology and Parasitology, University Clinic of Bonn, D-53105 Bonn, Germany.
Abstract:
A small peptide called PSM-mec is encoded on the type II, III and VIII SCCmec cassettes present in the genomes of nosocomial methicillin-resistant Staphylococcus aureus (MRSA) strains. This peptide is excreted by agr-positive strains, which represent about 89% of the strains of our collection and can be identified by the presence of delta toxin in mass spectrometry. The presence of the peptide in the MALDI-TOF MS spectra of whole cells was proved by a knock-down experiment employing a clone that expressed antisense RNA to psm-mec. Furthermore, evaluation of a collection of clinical agr-positive MRSA and MSSA isolates and type strains showed that, using a detection window of m/z 2411-2419, the PSM-mec is detected by mass spectrometry of whole cells with a sensitivity of 0.95 and a specificity of 1, thereby enabling rapid identification of a subgroup of MRSA with a method that is used during routine identification procedures.
Insights
A novel peptide, PSM-mec, can be detected using mass spectrometry in clinical samples. This method accurately identifies methicillin-resistant Staphylococcus aureus (MRSA) strains during routine procedures.
Area of Science:
- Microbiology
- Molecular Biology
- Analytical Chemistry
Background:
- The PSM-mec peptide is encoded on SCCmec cassettes in nosocomial MRSA strains.
- Agr-positive strains, common in MRSA, excrete PSM-mec, detectable via delta toxin in mass spectrometry.
- Routine identification methods need enhancement for specific MRSA detection.
Purpose of the Study:
- To confirm PSM-mec presence in MRSA using MALDI-TOF MS.
- To validate PSM-mec detection as a rapid identification method for MRSA.
- To assess the sensitivity and specificity of PSM-mec detection in clinical isolates.
Main Methods:
- Utilized a knock-down experiment with antisense RNA to confirm PSM-mec expression.
- Analyzed clinical isolates of MRSA and MSSA using MALDI-TOF MS.
- Defined a specific detection window (m/z 2411-2419) for PSM-mec in whole-cell mass spectra.
Main Results:
- PSM-mec presence was confirmed in MRSA strains via knock-down experiments.
- The defined mass spectrometry window accurately detected PSM-mec in 95% of MRSA and 100% of MSSA strains.
- This peptide detection method demonstrated high sensitivity (0.95) and specificity (1).
Conclusions:
- PSM-mec detection via MALDI-TOF MS is a reliable method for identifying MRSA.
- This technique can be integrated into routine identification procedures for rapid MRSA subgroup identification.
- The study provides a valuable tool for enhancing the diagnosis and management of MRSA infections.
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