Label‐free identification of antibiotic resistant isolates of living Escherichia coli: Pilot study

Abstract We introduce a label‐free spectroscopic method to classify subtypes of quinolone‐nonsusceptible Escherichia coli ( E. coli ) isolates obtained from human blood cultures. Raman spectroscopy with a 30‐nm gold‐deposited, surface‐enhanced Raman scattering (SERS) substrate was used to evaluate three multilocus sequencing typing (MLST)‐predefined groups including E . coli ATCC25922, E . coli ST131:O75, and E . coli ST1193:O25b. Although there was a coffee‐ring effect, the ring zone was selected at the ideal position to screen E. coli isolates. Strong Raman peaks were present at 1001–1004 cm −1 (CC aromatic ring breathing stretching vibrational mode of phenylalanine), 1447–1448 cm −1 (CH 2 scissoring deformation vibrational mode), and 1667 cm −1 (amide I α ‐helix). Although the three MLST‐predefined E . coli isolates had similar Raman spectral patterns, a support vector machine (SVM) learning algorithm‐assisted principal component analysis (PCA) analysis had superior performance in detecting the presence of quinolone‐nonsusceptible E. coli isolates as well as classifying similar microbes, such as quinolone‐nonsusceptible E . coli ST131:O75 and E . coli ST1193:O25b isolates. Therefore, this label‐free and nondestructive technique is likely to be useful for clinically diagnosing quinolone‐nonsusceptible E. coli isolates with the MLST method.