Detection of Escherichia coli O157:H7 and Salmonella Typhimurium Using Filtration followed by Fourier-Transform Infrared Spectroscopy†

Fourier-transform infrared spectroscopy has been successfully used as a nondestructive method for identifying, distinguishing, and classifying pathogens. In this study, a less time-consuming Fourier-transform infrared procedure was developed to identify Escherichia coli O157:H7 and Salmonella Typhimurium. Samples containing 109 CFU/ml were prepared in tryptic soy broth and then serially diluted (up to eight times) to obtain bacterial solutions of 109 to 10 CFU/ml. These dilutions were incubated at 37°C for 6 h, samples were filtered through a Metricel filter hourly (for 0 to 6 h), and spectra were obtained using a ZnSe contact attenuated total reflectance accessory on a Continuμm infrared microscope. Midinfrared spectra (4,000 to 700 cm−1)of Salmonella Typhimurium and E. coli O157:H7 were generated, and peak areas in the region of 1,589 to 1,493 cm−1 were used to detect the pathogens. Initially, detection limits were between 106 and 107 CFU/ml without preenrichment, and samples starting with 500 CFU/ml were detectable following incubation for 6 h, when counts reached at least 106 CFU/ml. Compared with results of previously published studies in which Fourier-transform infrared spectroscopy was used to identify select pathogens, this method is more rapid and less expensive for practical large-scale sample analysis.