Transcriptional and Phenotypic Responses of Listeria monocytogenes to Chlorine Dioxide

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Abstract
Significant food-borne disease outbreaks have occurred from consumption of ready-to-eat foods, including produce, contaminated withListeria monocytogenes. Challenging food matrices (e.g., cantaloupe, sprouts) with limited processing steps postharvest to reduce pathogen loads have underscored a need for new mitigation strategies. Chlorine dioxide (ClO2) is increasingly being used in produce and other food systems to reduce food-borne pathogen levels. The goal of this study was to characterize the transcriptional response and survival ofL. monocytogenes10403S exposed to ClO2. The transcriptional profile of log-phase cells exposed to 300 mg/liter ClO2for 15 min was defined by whole-genome microarray. A total of 340 genes were significantly differentially expressed. Among the differentially expressed genes, 223 were upregulated (fold change ≥ 1.5; adjustedPvalue < 0.05) in role categories responsible for protein fate, cellular processes, and energy metabolism. There were 113 and 16 genes differentially expressed belonging to regulatory networks of σBand CtsR, respectively. We assessedL. monocytogenes10403S survival after exposure to 100, 300, and 500 mg/liter aqueous ClO2in brain heart infusion (BHI) broth; there was a significant difference between cells exposed to 500 mg/liter ClO2and those exposed to all other conditions over time (Pvalue < 0.05). Isogenic ΔsigBand ΔctsRmutants exposed to 300 mg/liter ClO2were more sensitive to ClO2than the wild type under the same conditions. These results provide an initial insight into the mechanisms thatL. monocytogenesemploys to survive sublethal ClO2and further our understanding of the inactivation mechanisms of this increasingly used sanitizer.

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