Integrated metabolomics of big six Escherichia coli on pea sprouts to organic acid treatments

Naturally occurring organic acids (OAs) have demonstrated satisfactory effects in inhibiting common pathogens on fresh produce; however, their effectiveness on big six Escherichia coli serotypes, comprised of E. coli O26: H11, O45:H2, O103:H11, O111, O121:H19 and O145, remained unaddressed. Regarding this, using nuclear magnetic resonance (NMR) spectroscopy and ultra-high performance liquid chromatography-mass spectrometry (UPLC-MS), the sanitising efficacy and the underlying antimicrobial mechanisms of 10-min treatments with 0.2 mol/L ascorbic acid (AA), citric acid (CA) and malic acid (MA) against the big six strains on pea sprouts were thoroughly investigated in this study.Despite the varying antimicrobial efficacy (AA: 0.12-0.99, CA: 0.36-1.72, MA: 0.75-3.28 log CFU/g re-ductions), the three OAs induced consistent metabolic changes in the E. coli strains, particularly in the meta-bolism of membrane lipids, nucleotide derivatives and amino acids. Comparing all strains, the most OA-resistant strain, O26 (0.36-1.12 log CFU/g reductions), had the largest total amino acids accumulated to resist osmotic stress; its ulteriorly suppressed cell activity further strengthened its endurance. In contrast, the lowest OA-resistance of O121 (0.99-3.28 log CFU/g reductions) might be explained by the depletion of putrescine, an oxidative stress regulator. Overall, the study sheds light on the effectiveness of a dual-platform metabolomics investigation in elucidating the metabolic responses of big six E. coli to OAs. The manifested antimicrobial effects of OAs, especially MA, together with the underlying metabolic perturbations detected in the big six strains, provided scientific basis for applying OA treatments to future fresh produce sanitisation.

Automated summary

Naturally occurring organic acids (OAs) have shown satisfactory effects in inhibiting common pathogens on fresh produce, but their effectiveness against the big six Escherichia coli serotypes has not been addressed. In this study, the sanitizing efficacy and antimicrobial mechanisms of ascorbic acid (AA), citric acid (CA), and malic acid (MA) treatments on pea sprouts were investigated using nuclear magnetic resonance (NMR) spectroscopy and ultra-high performance liquid chromatography-mass spectrometry (UPLC-MS). The results showed that although the antimicrobial efficacy varied, the three OAs induced consistent metabolic changes in the E. coli strains, particularly in the metabolism of membrane lipids, nucleotide derivatives, and amino acids. The study highlights the effectiveness of a dual-platform metabolomics investigation in elucidating the metabolic responses of big six E. coli to OAs and provides a scientific basis for applying OA treatments to future fresh produce sanitization.