ABSTRACT

Agricultural water is a known source of contamination to fresh produce and can contain foodborne pathogens including Salmonella enterica, pathogenic Escherichia coli, Listeria monocytogenes, and Campylobacter jejuni. To mitigate such risks, antimicrobial agents such as hypochlorites and peroxyacetic acid (PAA) can be applied to in-line irrigation systems as well as to water used in postharvest washing. Although these compounds are effective and widely used, some pathogenic bacteria adapt to survive exposure. RNA sequencing was used to analyze the Salmonella Newport transcriptome after exposure to sodium hypochlorite (NaOCl) and PAA in a simulated agricultural water system. Overall cellular adaptive response was determined quantitatively as a function of overall gene expression of the >4,000 genes in the Salmonella Newport genome. Differentially expressed genes ranged from 11 due to 10-ppm NaOCl treatment, 316 due to 20-ppm NaOCl treatment, 1,719 due to 10-ppm PAA treatment, and 2,010 due to 20-ppm PAA treatment compared with that of the controls (water only). Differentially expressed transcripts included cellular functions such as biosynthesis, degradation, energy generation, and nonmetabolically linked functions. Oxidative exposure upregulated genes associated with key virulence, attachment, and gene transfer. Amino acid biosynthesis was upregulated due to NaOCl exposure but primarily downregulated when Salmonella Newport was exposed to PAA. Slight upregulation occurred in nucleoside and nucleotide biosynthesis, a known DNA repair mechanism seen during exposure to sanitizers. Our results indicate that Salmonella Newport reacts differently when exposed to NaOCl versus PAA, despite oxidative activity being the primary modes of antimicrobial action of both compounds.

HIGHLIGHTS
  • Peroxyacetic acid induced a more robust Salmonella response than hypochlorite.

  • Sanitizers upregulated genes involved in virulence, attachment, and gene transfer.

  • Sodium hypochlorite at 10 ppm did not elicit a significant stress response.

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