Summary auto-generated
This study presents intact cell mass spectrometry (ICMS) as a rapid method to distinguish methicillin-resistant Staphylococcus aureus (MRSA) from methicillin-sensitive S. aureus (MSSA). The technique analyzes intact bacterial cells using matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS), generating characteristic mass-to-charge spectra within minutes of sample preparation. Testing 20 staphylococcal isolates revealed that MSSA strains produced 37-67 peaks while MRSA strains produced 82-209 peaks, allowing clear visual discrimination between the two groups. Certain peaks were unique to MRSA or MSSA, while others were conserved across species or strains. The method demonstrated excellent reproducibility with over 90% peak reproduction across replicates. ICMS spectra also contained information useful for fine-level strain typing, comparable to pulsed-field gel electrophoresis. The authors conclude that ICMS offers potential for rapid MRSA identification in diagnostic laboratories, enabling faster treatment decisions and infection control interventions, though larger-scale trials were recommended to confirm these preliminary findings.
Key findings
- MSSA and MRSA strains were readily distinguished by peak patterns in ICMS spectra, with MRSA producing significantly more peaks (82-209) than MSSA (37-67)
- Certain mass-to-charge values were unique to MRSA or MSSA, while others were conserved across all staphylococcal species or individual strains
- Sample preparation and spectral analysis could be completed in minutes, allowing up to 10 isolates per hour to be analyzed and categorized
- ICMS spectra contained discrimination data at three levels: species identification, MRSA/MSSA classification, and fine-level strain typing comparable to conventional PFGE
- Reproducibility was excellent with over 90% peak reproduction across replicate analyses within isolates
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Abstract
Rapid, accurate discrimination between methicillin-sensitive Staphylococcus aureus (MSSA) and methicillin-resistant S. aureus (MRSA) strains is essential for appropriate therapeutic management and timely intervention for infection control. A rapid method involving intact cell mass spectrometry (ICMS) is presented that shows promise for identification, discrimination of MSSA from MRSA and typing. In ICMS, cells from a bacterial colony are emulsified in a chemical matrix, added to a sample slide, dried and analysed by matrix-assisted laser desorption ionisation time-of-flight mass spectrometry (MALDI-TOF-MS). This technique examines the chemistry of the intact bacterial cell surface, yielding spectra consisting of a series of peaks from 500 to 10 000, which represent the mass:charge (m:z) ratios. Each peak corresponds to a molecular fragment released from the cell surface during laser desorption. Specimens can be prepared in a few seconds from plate cultures and a spectrum can be obtained within 2 min. ICMS spectra for 20 staphylococcal isolates showed characteristic peaks, some of which were conserved at species level, some at strain level and some were characteristic of the methicillin susceptibility status of the strain. ICMS may have potential for MRSA identification and typing, and may improve infection control measures.