Fourier Transform Infrared (FTIR) spectroscopy provides a highly selective and reproducible means for the chemically-based
discrimination of intact microbial cells which make the method valuable for large-scale screening of foods. The
goals of the present study were to assess the effect of chemical interferents, such as food matrices, different sanitizing
compounds and growth media, on the ability of the method to accurately identify and classify L. innocua, L. welshimeri,
E. coli, S. cholerasuis, S. subterranea, E. sakazakii, and E. aerogenes. Moreover, the potential of FTIR spectroscopy for
discrimination of L. innocua and L. welshimeri of different genotypes and the effect of growth phase on identification
accuracy of L. innocua and L. welshimeri were tested. FTIR spectra were collected using two different sample
presentation techniques - transmission and attenuated total reflection (ATR), and then analyzed using multivariate
discriminant analysis based on the first derivative of the FTIR spectra with the unknown spectra assigned to the species
group with the shortest Mahalanobis distance. The results of the study demonstrated 100% correct identification and
differentiation of all bacterial strains used in this study in the presence of chemical interferents or food matrices, better
than 99% identification rate in presence of media matrices, and 100% correct detection for specific bacteria in mixed
flora species. Additionally, FTIR spectroscopy proved to be 100% accurate when differentiating between genotypes of L.
innocua and L. welshimeri, with the classification accuracy unaffected by the growth stage. These results suggest that
FTIR spectroscopy can be used as a valuable tool for identifying pathogenic bacteria in food and environmental samples.