Phenotypic and genotypic characterization of Canadian clinical isolates of Vibrio parahaemolyticus collected from 2000 to 2009

Abstract

Vibrio parahaemolyticus is the leading bacterial cause of food-borne illness due to the consumption of contaminated seafood. The aim of the present study was to determine the population of its subtypes and establish a better understanding of the various types of V. parahaemolyticus strains that are causing human illness in Canada. The subtypes for 100 human clinical isolates of V. parahaemolyticus collected between 2000 and 2009 were determined by performing serotyping, ribotyping, pulsed-field gel electrophoresis, and multilocus sequence typing. Within this panel of strains, there was a high level of diversity (between 22 and 53 subtypes per method), but the presence of predominant clones with congruent subtypes between the various methods was also observed. For example, all 32 isolates belonging to sequence type 36 (ST36) were from serogroup O4, while 31 of them were ribotype EcoVib235-287, and 24 of the 32 were SfiI pulsed-field gel electrophoresis (PFGE) pattern VPSF1.0001. With regard to the presence of known virulence genes, 74 of the 100 isolates were PCR positive for the presence of the thermostable direct hemolysin (tdh); and 59 of these 74 strains also contained the second virulence marker, the tdh-related hemolysin (trh). The detection of trh was more predominant (81%) among the clinical isolates, and only four (4%) of the clinical isolates tested negative for the presence of both tdh and trh. This database, comprising 100 clinical isolates of V. parahaemolyticus strains from Canada, forms a baseline understanding of subtype diversity for future source attribution and other epidemiologic studies.

FIG 1

Minimum spanning tree (MST) of multilocus sequence typing (MLST) of 100 clinical V. parahaemolyticus strains grouped by sequence types (ST) and combined with other types, such as ribotypes, pulsed-field gel electrophoresis (PFGE) patterns of chromosomal DNA digests (NotI, SfiI), and serotypes (color-coded). MST was created using BioNumerics version 6.5, and ST numbers are indicated in the middle of the nodes. The lines infer relatedness by stating the number of differing alleles, and an unattached node has no alleles in common with the STs in the tree. The node sizes are related to the number of isolates, and the gray border around nodes indicates clonal complex (CC).