Dynamic insights into increasing antibiotic resistance in Staphylococcus aureus by label-free SERS using a portable Raman spectrometer

•This study dynamically monitored antibiotic-derived resistance using a portable Raman spectrometer.•The molecular changes in drug-resistant strains can be rapidly and sensitively recorded by SERS in a whole-cell manner.•PC-LDA applied to bacterial SERS profiles can correctly distinguish among varying degree of resistant strains.•The MIC value showed a non-linear correlation with I734/I867, and R2 reached above 0.90.•SERS results were consistent with the K−B test, MIC determination, and PCR results.