Rapid detection of B2-ST131 clonal group of extended-spectrum β-lactamase-producing Escherichia coli by matrix-assisted laser desorption ionization-time-of-flight mass spectrometry: discovery of a peculiar amino acid substitution in B2-ST131 clonal group.

One reason for the spread of extended-spectrum β-lactamase (ESBL)-producing Escherichia coli worldwide is the global pandemic of the B2-ST131 clonal group. We searched for the specific biomarker peaks to distinguish between the B2-ST131 clonal group and other sequence type (ST) clonal groups isolated from clinical specimens obtained in our hospital. Biomarker peaks at m/z 7650 in the B2-ST131 group (sensitivity of 100% and specificity of 89.7%) and m/z 7707 in the other ST clonal groups showed the highest discrimination abilities. We further verified reproducibility against other Japanese clinical isolates obtained in another area of Japan. Differences between the molecular mass at the 7650m/z and 7707m/z peaks indicated an E34A amino acid substitution by proteomic and genomic analysis. Matrix-assisted laser desorption ionization-time-of-flight mass spectrometry rapidly and simply identified the B2-ST131 clonal group in routine examinations and will allow for adequate empirical therapy and the possibility to control both hospital infections and the global pandemic.