Methicillin-resistant Staphylococcus aureus (MRSA) is a well-known superbug that has the staphylococcal cassette chromosome mec, a mobile genetic element containing genes that enable resistance to β-lactam antibiotics. Specifically, the mecA gene encodes the penicillin-binding protein PBP2a involved in peptidoglycan biosynthesis, cell-wall formation and resistance to antibiotics. MRSA can be categorized into 13 genotypes that differ in their susceptibility to antibiotics, and PBP2a differs between genotypes. Multiple methods are available for the identification of bacterial genotypes by PCR, but they usually require the lysis of bacterial cells and isolation of nucleic acids. Hu et. al. developed a sensor array for the identification of different MRSA strains on the basis of changes in fluorescence. They synthesized eight fluorescent probes that contained the same core scaffold decorated with diverse pairs of quaternary ammonium salts. The probes emit either blue fluorescence or red fluorescence depending on their conformation. As genotypically distinct MRSA strains have different levels of PBP2a expression, the content and morphology of negatively charged cell-wall components consequently vary as well. Positively charged fluorescent probes thus interact differently with bacterial cell walls from distinct genotypes, which causes conformational changes and different blue/red fluorescence intensity ratios. The ratios are measured in a microplate reader, followed by statistical analysis, which results in a specific fingerprint for each bacterial strain tested. The authors showed that their sensor array can be used for differential sensing of Gram-positive and Gram-negative bacteria and clinically relevant superbugs, in addition to MRSA. The results were in good agreement with those obtained via PCR. Because of its simplicity and practicality, the sensor array could be used for point-of-care diagnostics without the need for isolation of nucleic acids before analysis.
Original reference: J. Am. Chem. Soc. 145, 8917–8926 (2023)
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