Transcriptomic Analysis of Listeria monocytogenes Grown on Refrigerated Cantaloupe Slices

Introduction: The foodborne pathogen Listeria monocytogenes has been associated with a variety of foods. Prior to a successful foodborne transmission to a human host, the pathogen has to adapt in a specific food through modulation of its gene expression in order to ensure its survival and growth in foods. Understanding of the pathogen’s response to diverse food environments is imperative to devise effective control strategies as well as elucidate potential impact of foods on virulence potential.

Purpose: The purpose of this study was to assess transcriptional response of L. monocytogenes during growth in refrigerated cantaloupe.

Methods: The transcriptional profiles of L. monocytogenes grown to stationary phase in cantaloupe slices or brain heart infusion (BHI) under refrigeration were compared by a custom-designed microarray. The microarray was designed to represent 16,724 annotated gene sequences from 41 closed chromosomes of L. monocytogenes, 5 plasmids, and 16 whole genome shotgun sequences which were available from GenBank as of April, 2014.

Results: A total of 216 and 181 genes were significantly up- and downregulated in L. monocytogenes grown in cantaloupe as compared to BHI (fold change ≥ 2.5 and FDR < 0.05). Majority of the upregulated genes belonged to functions related to amino acid and nucleotide transport and metabolism while the majority of downregulated genes belonged to carbohydrate transport and metabolism. Interestingly, transcript levels of several stress- and virulence-related genes were significantly altered, implying the potential impact of growth in cantaloupe slices on stress resistance and virulence potential of L. monocytogenes.

Significance: Evaluation of transcriptional landscape of L. monocytogenes during growth in foods such as cantaloupe is an effective approach to determining how the pathogen adapts and grows in complex food systems. The resulting knowledge has the potential to facilitate development of novel control strategies as well as improved risk assessment.