Abstract
Disease outbreaks of verotoxin-producing Escherichia coli (VTEC) O157:H7 and non-O157 serotypes associated with leafy green vegetables are becoming a growing concern. A better understanding of the behavior of VTEC, particularly non-O157 serotypes, on lettuce under stress conditions is necessary for designing more effective control strategies. Hydrogen peroxide (H2O2) can be used as a sanitizer to reduce the microbial load in leafy green vegetables, particularly in fresh produce destined for the organic market. In this study, we tested the hypothesis that H2O2 treatment of contaminated lettuce affects in the same manner transcription of stress-associated and virulence genes in VTEC strains representing O157 and non-O157 serotypes. Six VTEC isolates representing serotypes O26:H11, O103:H2, O104:H4, O111:NM, O145:NM, and O157:H7 were included in this study. The results indicate that 50 mM H2O2 caused a population reduction of 2.4–2.8 log10 (compared to non-treated control samples) in all six VTEC strains present on romaine lettuce. Following the treatment, the transcription of genes related to oxidative stress (oxyR and sodA), general stress (uspA and rpoS), starvation (phoA), acid stress (gadA, gadB, and gadW), and virulence (stx1A, stx2A, and fliC) were dramatically downregulated in all six VTEC serotypes (P ≤ 0.05) compared to not treated control samples. Therefore, VTEC O157:H7 and non-O157 serotypes on lettuce showed similar survival rates and gene transcription profiles in response to 50 mM H2O2 treatment. Thus, the results derived from this study provide a basic understanding of the influence of H2O2 treatment on the survival and virulence of VTEC O157:H7 and non-O157 serotypes on lettuce.
Highlights
Verotoxin-producing Escherichia coli (VTEC), referred to as Shiga toxin (Stx)-producing E. coli (STEC), often cause life-threatening diseases, such as hemorrhagic colitis (HC) and hemolytic uremic syndrome (HUS) (Croxen et al, 2013; Karpman and Stahl, 2014; Karmali, 2017)
Treatment of contaminated lettuce with 50 mM H2O2 for 40 min reduced the populations of all verotoxin-producing Escherichia coli (VTEC) strains tested in this study by 2.4–2.8 log10 (Table 2)
This study focused on well-known virulence genes including genes encoding intimin, Stx genes stx1A and stx2A and flagellin genes (Figures 1–6)
Summary
Verotoxin-producing Escherichia coli (VTEC), referred to as Shiga toxin (Stx)-producing E. coli (STEC), often cause life-threatening diseases, such as hemorrhagic colitis (HC) and hemolytic uremic syndrome (HUS) (Croxen et al, 2013; Karpman and Stahl, 2014; Karmali, 2017). More than 70% of infections linked to nonO157 VTEC were caused by serotypes O26, O45, O103, O111, O121, and O145 (termed the Top 6; Saito et al, 1998; Brooks et al, 2005; Folster et al, 2011; Bradley et al, 2012; Brown et al, 2012). In 2011, enteroaggregative E. coli O104:H4 caused the biggest outbreak in Germany. This strain produces Stx and is one of the most virulent strains of non-O157 VTEC (Buchholz et al, 2011; Zangari et al, 2013; Karmali, 2017)
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