The mechanisms that regulate Vibrio parahaemolyticus virulence gene expression differ between pathotypes.

Nicholas Petronella,Jennifer Ronholm

doi:10.1099/mgen.0.000182

Nicholas Petronella, Jennifer Ronholm

Open Access

https://doi.org/10.1099/mgen.0.000182

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Journal: Microbial genomics	Publication Date: May 29, 2018
Citations: 5	License type: CC BY 4.0

Affiliation: McGill University, Health Canada

Abstract

Most Vibrio parahaemolyticus isolates found in marine environments are non-pathogenic; however, certain lineages have acquired genomic pathogenicity islands (PAIs) that enable these isolates to cause human illness. The V. parahaemolyticus PAI contains one or both of two toxins: thermostable direct haemolysin (TDH) or TDH-related haemolysin (TRH) and type III secretion system 2 (T3SS2). Recently, a few V. parahaemolyticus isolates that do not have this PAI were obtained from clinical samples, and there has been interest in determining whether these isolates possess novel virulence factors. In this investigation, we have selected four V. parahaemolyticus isolates: a canonical pathogenic strain containing TDH, TRH and T3SS2; two strains from clinical cases which do not contain a PAI; and an environmental isolate which also does not contain a PAI. For each isolate, we analyzed differential gene expression after crude bile exposure. Several enteric bacterial pathogens are known to use bile as a signal to enhance virulence gene expression. We have shown that in the tdh-positive trh-positive pathotype gene virulence gene expression was not up-regulated in response to crude bile, strongly indicating that the current dogma of virulence gene regulation in V. parahaemolyticus needs to be revisited and separately investigated for each pathotype. In addition, we have created a list of genes of interest that were up-regulated in the non-canonical pathotypes which may contribute to virulence in these isolates.

Highlights

Vibrio parahaemolyticus is a Gram-reaction-negative, halophilic bacterium that naturally occurs in marine environments, including estuaries
T3SS2 derives from two separate genetic lineages: T3SS2a is typically found in association with the tdh gene, while T3SS2b is found in lineages that contain either the trh or both the trh and tdh genes [12]
To identify genes that were differentially expressed in TSB3N cultures and during crude bile exposure we compared the RNA-seq data for these conditions using CuffDiff, which is a package within the Cufflinks software, that allows for differential expression analysis with RNA-seq data [38]

Summary

Introduction

Vibrio parahaemolyticus is a Gram-reaction-negative, halophilic bacterium that naturally occurs in marine environments, including estuaries. Most V. parahaemolyticus strains are non-pathogenic, some have acquired virulence factors that can result in human illness when individuals are exposed through the consumption of contaminated seafood [1]. Pathogenic V. parahaemolyticus isolates are differentiated from their non-pathogenic counterparts by the presence of several virulence factors. Pathogenic isolates generally have at least one of two major toxigenic virulence factors, thermostable direct haemolysin (TDH) [3] and TDH-related haemolysin (TRH) [4]. All V. parahaemolyticus isolates contain a type III secretion system (T3SS) commonly called T3SS1, and pathogenic strains typically contain a second T3SS called T3SS2 [8]. T6SS2 is found in all V. parahaemolyticus strains, while T6SS1 is mostly associated with clinical isolates, and may play a role in virulence [13, 14]. On the basis of the presence or absence of different virulence genes each clinical V. parahaemolyticus isolate can be assigned to one of four pathotypes (Table 1) [16]

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