FTIR-assisted MALDI-TOF MS for the identification and typing of bacteria.

MALDI-TOF MS is well-recognized for microbial identification and widely used in research and clinical fields due to its specificity, speed of analysis, and low cost of consumables. However, the classification or identification accuracy is poor for E. coli and Shigella. In addition, FTIR is a promising tool for bacterial typing. In this study, 14 strains of E. coli and 9 strains of Shigella were typed by both MALDI-TOF MS and FTIR techniques. Alternatively, a data fusion strategy using these two approaches was attempted to achieve better typing accuracy. Hierarchical clustering analysis (HCA) revealed that the typing accuracies for selected E. coli and Shigella from blood agar were 65.2%, 78.3%, and 100% for MALDI-TOF MS, FTIR, and FTIR combined with MALDI-TOF MS, respectively. Based on these results, a library constructed of the MS-IR fusion data was employed to identify individual bacteria at the strain level, and the library-based typing accuracies for 207 test spectra of sample strains from three different culture media yielded 97.6% accuracy for distinguishing between E. coli and Shigella at genus level. For species level and strain level, it yielded 95.2% and 92.3% typing accuracy, respectively. These results indicate that FTIR is a better technique for typing selected E. coli and Shigella than MALDI-TOF MS, and the accuracy is increased by combining the data from MALDI-TOF MS and FTIR spectroscopy. FTIR could be used to supplement MALDI-TOF MS for the identification and typing of taxonomic microorganisms.