Rapid discrimination between methicillin-sensitive and methicillin-resistant Staphylococcus aureus by intact cell mass spectrometry

Rapid, accurate discrimination between methicillin-sensitive Staphylococcus aureus (MSSA) and methicillin-resistant S, aureus (MRSA) strains is essent ial for appropriate therapeutic management and timely intervention for infe ction control. A rapid method involving intact cell mass spectrometry (ICMS ) is presented that shows promise for identification, discrimination of MSS A from MRSA and typing. In ICMS, cells from a bacterial colony are emulsifi ed in a chemical matrix, added to a sample slide, dried and analysed by mat rix-assisted laser desorption ionisation time-of-flight mass spectrometry ( MALDI-TOF-MS), This technique examines the chemistry of the intact bacteria l cell surface, yielding spectra consisting of a series of peaks from 500 t o 10000, which represent the mass:charge (m:z) ratios, Each peak correspond s to a molecular fragment released from the cell surface during laser desor ption, 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 speci es level, some at strain level and some were characteristic of the methicil lin susceptibility status of the strain. ICMS may have potential for MRSA i dentification and typing, and may improve infection control measures.