Transcriptome analysis of Listeria monocytogenes exposed to biocide stress reveals a multi-system response involving cell wall synthesis, sugar uptake, and motility

Abstract

Listeria monocytogenes is a virulent food-borne pathogen most often associated with the consumption of “ready-to-eat” foods. The organism is a common contaminant of food processing plants where it may persist for extended periods of time. A commonly used approach for the control of Listeria monocytogenes in the processing environment is the application of biocides such as quaternary ammonium compounds. In this study, the transcriptomic response of a persistent strain of L. monocytogenes (strain 6179) on exposure to a sub-lethal concentration of the quaternary ammonium compound benzethonium chloride (BZT) was assessed. Using RNA-Seq, gene expression levels were quantified by sequencing the transcriptome of L. monocytogenes 6179 in the presence (4 ppm) and absence of BZT, and mapping each data set to the sequenced genome of strain 6179. Hundreds of differentially expressed genes were identified, and subsequent analysis suggested that many biological processes such as peptidoglycan biosynthesis, bacterial chemotaxis and motility, and carbohydrate uptake, were involved in the response of L. monocyotogenes to the presence of BZT. The information generated in this study further contributes to our understanding of the response of bacteria to environmental stress. In addition, this study demonstrates the importance of using the bacterium's own genome as a reference when analysing RNA-Seq data.

TheListeria monocytogenestransposon Tn6188provides increased tolerance to various quaternary ammonium compounds and ethidium bromide

“…Presence of the gene pair ykkCD was shown to increase tolerance to, for example, EtBr, CPC, crystal violet and tetracycline in E. coli (Jack et al ., ). Increased expression of qacH , ykkC , lmrB , ykkD and other transporters as well as many genes involved in various biological functions has recently been reported when L. monocytogenes 6179 was exposed to sublethal concentrations of BZT (Casey et al ., ).…”

“…Usage of more than one reference gene will improve reliability; nevertheless, the 16S rRNA gene was the most stably expressed housekeeping gene in L. monocytogenes in a study conducted by Tasara and Stephan (Tasara & Stephan, ). Furthermore, our results are confirmed by a recent study using RNAseq of L. monocytogenes 6179 (harbouring a Tn 6188 copy, which is identical to Tn 6188 from strain 4423), which showed a fourfold upregulation of qacH in the presence of BZT (Casey et al ., ) – similar to what we observe here. Although qRT‐PCR supports our MIC data that QacH's substrate spectrum comprises various QACs, indirect effects during deletion and complementation may influence MICs.…”

Transcriptome Sequencing of Listeria monocytogenes Reveals Major Gene Expression Changes in Response to Lactic Acid Stress Exposure but a Less Pronounced Response to Oxidative Stress

“…It possesses a 3.01 Mbp genome and a 62.2 kbp plasmid, designated pLM6179 (Schmitz-Esser et al, 2015b). Notably, the stress survival characteristics of L. monocytogenes 6179 have been extensively characterized (Müller et al, 2013(Müller et al, , 2014Casey et al, 2014;Makariti et al, 2015;Rychli et al, 2016;Harter et al, 2017;Naditz et al, 2019). L. monocytogenes strain R479a is an ST8 strain isolated from smoked salmon in Denmark in 1996 where it persisted for more than 2 years in the same FPE (Fonnesbech Vogel et al, 2001;Schmitz-Esser et al, 2015a).…”

“…Upon exposure to environmental stress conditions found in food and FPEs, L. monocytogenes responds by activating a wide variety of mechanisms that confer stress tolerance (Dutta et al, 2013;Müller et al, 2013;Harter et al, 2017;Bucur et al, 2018;Hingston et al, 2019). In addition to functional characterization, multiple gene expression analyses have implicated many genes in the response of L. monocytogenes to temperature, oxidative, disinfectant, pH, and osmotic stresses (Oliver et al, 2009;Soni et al, 2011;Tessema et al, 2012;Casey et al, 2014;Tang et al, 2015;Hingston et al, 2017b). Until now, transcriptomic research on L. monocytogenes has been conducted almost exclusively on strains that lack plasmids.…”

Listeria and -Omics Approaches for Understanding its Biology

“…To better understand how these strains are able to tolerate the detergents encountered in the food processing environment, the transcriptome responses of persistent and nonpersistent isolates to a sublethal dose of the QAC benzethonium chloride were analyzed (Casey et al, 2014;Fox et al, 2011). A comparison of the transcriptome of the L. monocytogenes persister strain 6179 in the presence and absence of benzethonium chloride showed that genes involved in peptidoglycan biosynthesis, carbohydrate uptake, chemotaxis, and motility were overexpressed (Casey et al, 2014). A comparison of the transcriptome of the L. monocytogenes persister strain 6179 in the presence and absence of benzethonium chloride showed that genes involved in peptidoglycan biosynthesis, carbohydrate uptake, chemotaxis, and motility were overexpressed (Casey et al, 2014).…”