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Development of a More Sensitive and Specific Chromogenic Agar Medium for the Detection of Vibrio parahaemolyticus and Other Vibrio Species
Published on: November 8, 2016
The mechanisms that regulate Vibrio parahaemolyticus virulence gene expression differ between pathotypes
Nicholas Petronella1, Jennifer Ronholm2,3
11Biostatistics and Modelling Division, Bureau of Food Surveillance and Science Integration, Food Directorate, Health Canada, Ottawa, ON, 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.
Insights
Most Vibrio parahaemolyticus are non-pathogenic, but some acquire genomic pathogenicity islands (PAIs). This study reveals bile does not up-regulate virulence genes in canonical strains, suggesting new virulence factors in non-canonical strains warrant investigation.
Area of Science:
- Microbiology
- Genomics
- Bacterial Pathogenesis
Background:
- Most Vibrio parahaemolyticus from marine environments are non-pathogenic.
- Pathogenic strains possess genomic pathogenicity islands (PAIs) encoding toxins like TDH/TRH and T3SS2.
- Non-canonical V. parahaemolyticus isolates lacking PAIs have been found in clinical settings, prompting research into novel virulence factors.
Purpose of the Study:
- To investigate differential gene expression in V. parahaemolyticus isolates with varying pathogenic profiles upon exposure to crude bile.
- To determine if bile acts as a virulence gene expression signal in different V. parahaemolyticus pathotypes.
- To identify potential novel virulence factors in non-canonical V. parahaemolyticus isolates.
Main Methods:
- Comparative analysis of gene expression in four V. parahaemolyticus isolates: one canonical pathogenic strain (TDH, TRH, T3SS2 positive) and three non-canonical strains (two clinical, one environmental) lacking PAIs.
- Exposure of isolates to crude bile to assess its effect on virulence gene expression.
- Differential gene expression analysis to identify up-regulated genes in response to bile.
Main Results:
- Virulence gene expression was not up-regulated by crude bile in the canonical TDH-positive, TRH-positive V. parahaemolyticus strain.
- This finding challenges the established understanding of bile as a universal virulence signal in V. parahaemolyticus.
- Several genes of interest were identified as up-regulated in the non-canonical V. parahaemolyticus pathotypes exposed to bile, suggesting potential novel virulence mechanisms.
Conclusions:
- The regulation of virulence genes by bile in V. parahaemolyticus is pathotype-specific and requires further investigation.
- The current dogma regarding bile-induced virulence gene expression in V. parahaemolyticus needs revision.
- The identified up-regulated genes in non-canonical isolates represent promising candidates for novel virulence factors contributing to V. parahaemolyticus pathogenesis.
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