Fourier transform infrared (FT-IR) spectroscopy, a novel technique to study the biochemical structure of bacterial cells

This research work was performed to examine the feasibility of using Fourier transform infrared (FT-IR) spectroscopy (in the mid-IR range, 4000-400 cm-1) to (i) detect and identify Pseudomonas aeruginosa and Escherichia coli in bottled drinking water; (ii) identify and detect E. coli O157:147 and Alicyclobacillus spp. recovered from apple juice; (iii) discriminate intact from pH, heat, and salt treated E. coli and Listeria innocua; and (iv) detect the biochemical changes in E. coli and L. innocua that occur during growth in batch culture.; The greatest spectral variation was observed between 1800 cm-1 and 900 cm-1: for amide I band at ∼1650 cm -1, amide II band at ∼1540 cm-1, CH3 and CH2 of protein components around 1455 cm-1 and 1398 cm-1, P=O of the phosphodiester backbone of nucleic acids around 1242 cm-1 and 1080 cm-1, and polysaccharide compounds around 1050--950 cm-1. Regarding the drinking water experiment, principal component analysis (PCA) demonstrated that bacterial cells were noticeably segregated. Using soft independent modeling of class analogy (SIMCA), 53 out of 60 spectra (88.3%) of E. coli ATCC 25922, 50 out of 60 spectra (83.3%) of P. aeruginosa, and 50 out of 60 spectra (83.3%) of the mixed culture (E. coli and P. aeruginosa) were correctly classified. In case of the apple juice experiment, loadings 1 and 2 of the PCA were representative of the bacterial spectral data and accounted for 73% of the total variability, treatments were noticeably segregated with distinct clustering by PCA. From the second derivative transformation and loadings plot, FT-IR showed the potential to discriminate intact from pH, heat, and salt treated E. coli and L. innocua and discriminate between selected types and degrees of cell inhibitory treatment. FT-IR spectroscopy with association of PCA, and SIMCA procedures could detect the changes in the cellular structure of bacterial cells (the variations in nucleic acids, proteins, lipids, and polysaccharides) that occur during the growth phases.; These results indicate that FT-IR spectroscopy can be used to detect, identify, and discriminate between bacterial cells based on the differences in genetic and phenotypic characteristics of bacteria with the help of multivariate analysis methods.