Detection of extended-spectrum-β-lactamase-producing Escherichia coli ST131 and ST405 clonal groups by matrix-assisted laser desorption ionization-time of flight mass spectrometry.

Escherichia coli sequence type 131 (ST131) and ST405 are important clonal groups, because they are associated with the global increase of extended-spectrum-β-lactamase (ESBL) producers. Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) is emerging as a rapid, inexpensive, and accurate method for bacterial identification. We investigated the detection performance of MALDI-TOF for the ST131 and ST405 clonal groups using 41 ST131-O25b, 26 ST131-O16, and 41 ST405 ESBL-producing isolates and 41 ESBL-producing isolates frrom other STs. The main spectra representing each clonal group were used for classification with Biotyper (Bruker Daltonics GmbH, Bremen, Germany). The peak that had the highest area under the receiver-operating characteristic curve generated by ClinProTools (Bruker) was detected with FlexAnalysis (Bruker), and an optimal signal-to-noise ratio cutoff was determined. The optimal detection models were generated by ClinProTools. Classification by Biotyper could detect the ST131-whole (O25b and O16 together) group with a sensitivity of 98.5% and a specificity of 93.9%. With FlexAnalysis, a peak of 9,720 Da detected the ST131-whole group with a sensitivity of 97.0% and a specificity of 91.5% at a cutoff value of 8.0. The ClinProTools models exhibited good performance for the detection of the ST131-whole group (sensitivity and specificity, 94.0% and 92.7%, respectively), the ST131-O25b group (95.1% and 98.2%, respectively), and the ST405 group (90.2% and 96.3%, respectively). MALDI-TOF MS had high detection performance for the ST131-whole, ST131-O25b, and ST405 clonal groups. MALDI-TOF MS should be considered as an alternative method to monitor the epidemiology of the ESBL-producing E. coli ST131 and ST405 clonal groups.