Synergistic action of electrolyzed water and mild heat for enhanced microbial inactivation of Escherichia coli O157:H7 revealed by metabolomics analysis

Abstract

To determine the bactericidal mechanism of electrolyzed water and mild heat against Escherichia coli O157:H7, we performed ultra-performance liquid chromatography quadrupole time of flight mass spectrometry (UPLC-qTOF-MS/MS) coupled with multivariate analysis to profile the intracellular metabolites of E. coli O157:H7 in response to electrolyzed water (EW) and mild heat treatment. The results indicated that EW (4 mg/L free available chlorine) combined with heat treatment at 50 °C resulted in 2.31 log CFU/mL reduction of E. coli O157:H7 and the reactive oxygen species fluorescence intensity of EW at 50 °C was ten times higher than that of the control group. Data demonstrated that treatment with EW and heat caused significant perturbation of metabolic pathways that were functionally related with amino acid metabolism, nucleotides synthesis, and lipid biosynthesis. EW at 50 °C resulted in major alterations to pathways involved in acyl carrier protein metabolism, anhydromuropeptides recycling, biosynthesis of CDP-diacylglycerol, trehalose and lipid IVa. Transcriptome analysis revealed that heat and EW affected the transcription levels of some genes in opposite ways. The expression of rpoS, oxyR, soxR, gadA, gadB, sucA, and sucB in the 50 °C group was downregulated, but upregulated in EW exposed cells. The expression of most genes was reduced in response to the combined treatment, with 0.024- and 0.286-fold downregulation of udk (encoding uridine kinase) and gadA (encoding glutamate decarboxylase alpha), respectively, being observed in cells treated with EW at 50 °C. These results provided further evidence of the metabolomic and transcriptomic response of E. coli O157:H7 to oxidation and heat stress.