DNA-based surrogate indicator for sanitation verification and predict inactivation of Escherichia coli O157:H7 using vibrational spectroscopy (FTIR)

Washing and sanitation of fresh produce and food contact surfaces are vital steps in reducing the risk of food-borne illness. However, there is a lack of process control and verification tools to directly assess reduction of bacteria during a sanitation process. The overall goal of this study was to evaluate DNA as a biochemical surrogate indicator to assess sanitation process. Structural and chemical changes in DNA molecules immobilized on a membrane surface (DNA@Anodisc) and suspended in an aqueous solution (In-Liquid-DNA) were assessed using vibrational spectroscopy and chemometric analysis by a comparison between isolated DNA and the DNA in live Escherichia coli O157:H7 cells. The results of Fourier Transform Infrared (FTIR) illustrate DNA oxidation, fragmentation and conformational changes from double-stranded (ds) to single-stranded (ss) DNA. The PCA model was able to discriminate different groups of samples which were exposed to different concentrations of chlorine (non-lethal, sub-lethal, and lethal; 0, 2, 5, 10, and 15 ppm). PLSR model results showed that the degree of DNA oxidation could be quantified and used successfully to predict the chlorine concentrations and bacterial count. The regression coefficient for predicted vs measured chlorine concentrations and bacterial count were satisfying for all treatments (R-2 > 0.96). The results also showed that the extent of oxidation and fragmentation of DNA was relatively higher for the In-Liquid-DNA, compared to the DNA@Anodisc, and E. coli. The results also suggest that the impact of the chlorine on the DNA@Anodisc and the DNA in the E. coli cells were similar compared to the In-liquid DNA. Overall, these studies illustrate the potential of DNA based biochemical surrogate indicator for sanitation process validation of food contact surfaces and fresh produce and demonstrate effectiveness of a chemometric spectral approach for these measurements.