Purpose: The purpose of this study was to investigate the lethal and sublethal injury in L. monocytogenes and L. innocua after LcEW treatments and to characterize the metabolic profile changes and the affected pathways using nuclear magnetic resonance (NMR).
Methods: The efficacy of LcEW in inactivating L. monocytogenes and L. innocua was evaluated by direct plating on non-selective and selective media. The metabolomic extracts from L. innocua were investigated by NMR coupled with multivariate analysis.
Results: The sublethally injured cells of L. monocytogenes and L. innocua increased from 43.65% to 78.21% and 36.26% to 63.69%, respectively, when the free available chlorine (FAC) of LcEW increased from 0.5 to 8 mg/L. In total, 36 low molecular weight metabolic compounds in L. innocua extracts were detected by NMR spectroscopy coupled with multivariate analysis, indicating complex response to oxidative perturbation on the metabolic level. LcEW (4 mg/L FAC) caused significant elevation of 3-hydroxybutyrate, succinate, fumarate, malate, and α-ketoglutarate, but decrease of nucleotides (cytidine, uridine), amino acids (valine, tyrosine, alanine) and ribose-5-phosphate levels. The findings indicated that EW stress severely disturbed the nucleotide and amino acid biosynthesis, energy-associated metabolism, osmotic regulation, and cell wall mucopeptide synthesis.
Significance: This study provided direct evidence that EW at sublethal levels induced oxidative stress in microorganism. The study, also, identified the EW associated metabolic changes in L. innocua. These cellular metabolite results might serve as a basis for future mechanistic studies.