Purpose: The purpose of this study was to evaluate the discrimination approach of the major EHEC, serovar O157, O26, O111 and the others by MALDI-TOF MS based on S10-GERMS method.
Methods: Totally twenty-nine O157, six O26 and two O111 strains, seven EHEC strains with another serovars, and sixteen non-EHEC strains were obtained from culture collections. First, the observed m/z values were obtained by MALDI-TOF MS analysis of the genome-sequenced strains. Second, the theoretical m/z values of ribosomal proteins in S10-spc-alpha operon were calculated by determination of the DNA sequence or sequence data obtained from NCBI database for genome-sequenced strains and then verified by comparison with the observed m/z values. The EHEC-specific protein peaks were selected as biomarkers for the in-house classification tool which has been developed based on S10-GERMS method. To verify the accuracy and reproducibility of discrimination with the selected biomarkers, sixteen O157 strains isolated from food samples were analyzed with the various expected sample conditions in daily analysis.
Results: We demonstrated semi-automated pattern matching classification with in-house classification tool with binary matrix using the selected four biomarkers and thirty-seven O157, O26 and O111 strains were successfully classified as proper serovar groups with 100% reliability. Sixteen O157 strains from food samples were successfully determined as O157 by general MALDI-TOF MS analysis either with sinapic acid or CHCA as matrix.
Significance: The discrimination method for major EHEC, O157, O26 and O111 was established based on the S10-GERMS method by using four biomarkers observed in MALDI-TOF MS analysis. This approach allows rapid screening of E. coli O157, O26 and O111 from the others by a routine MALDI-TOF MS analysis regardless of the sample condition.