Genetic Relationships of Vibrio parahaemolyticus Isolates from Clinical, Human Carrier, and Environmental Sources in Thailand, Determined by Multilocus Sequence Analysis

Abstract

e Vibrio parahaemolyticus is a seafood-borne pathogenic bacterium that is a major cause of gastroenteritis worldwide. We investigated the genetic and evolutionary relationships of 101 V. parahaemolyticus isolates originating from clinical, human carrier, and various environmental and seafood production sources in Thailand using multilocus sequence analysis. The isolates were recovered from clinical samples (n ‫؍‬ 15), healthy human carriers (n ‫؍‬ 18), various types of fresh seafood (n ‫؍‬ 18), frozen shrimp (n ‫؍‬ 16), fresh-farmed shrimp tissue (n ‫؍‬ 18), and shrimp farm water (n ‫؍‬ 16). Phylogenetic analysis revealed a high degree of genetic diversity within the V. parahaemolyticus population, although isolates recovered from clinical samples and from farmed shrimp and water samples represented distinct clusters. The tight clustering of the clinical isolates suggests that disease-causing isolates are not a random sample of the environmental reservoir, although the source of infection remains unclear. Extensive serotypic diversity occurred among isolates representing the same sequence types and recovered from the same source at the same time. These findings suggest that the O-and K-antigen-encoding loci are subject to exceptionally high rates of recombination. There was also strong evidence of interspecies horizontal gene transfer and intragenic recombination involving the recA locus in a large proportion of isolates. As the majority of the intragenic recombinational exchanges involving recA occurred among clinical and carrier isolates, it is possible that the human intestinal tract serves as a potential reservoir of donor and recipient strains that is promoting horizontal DNA transfer, driving evolutionary change, and leading to the emergence of new, potentially pathogenic strains. Vibrio parahaemolyticus is a seafood-borne pathogenic bacterium and is the leading cause of traveler's diarrhea and gastroenteritis worldwide due to the consumption of undercooked contaminated seafood, particularly shellfish. The organism possesses a number of virulence factors, including a thermostable direct hemolysin (TDH) (1), a thermostable direct hemolysinrelated hemolysin (TRH) (2), and type 3 secretion system 1 (TTSS1) and TTSS2 (3). Strains that possess tdh, trh, and TTSS2-encoding genes are generally pathogenic and responsible for the vast majority of clinical cases. While such strains account for only 1 to 2% of isolates sampled from water and different marine species (4-6), they are known to have a widespread global distribution, having been reported from cases of infection in Japan, India, Thailand, Malaysia, China, Indonesia, the United Kingdom, Italy, and the East and Gulf Coasts of the United States (7-19).The public health and commercial burdens associated with V. parahaemolyticus contamination are very high in Thailand due to the wide consumption of seafood. Although undercooked seafood has been identified as a source of V. parahaemolyticus infection (20, 21), the relative likelihood of contamination from differ...

Population analysis of Vibrio parahaemolyticus originating from different geographical regions demonstrates a high genetic diversity

“…These observations correspond to previous investigations and are typical for epidemic populations [13,15,23,24,27]. In these populations clones emerge from a background of recombinogetic bacteria occasionally and are able to spread [53].…”

“…[24]. These pSTs represent a large number of different STs of various geographic origins (pST1 corresponds to 142 STs and pST2 to 127 STs).…”

Aggressive Emerging Pathovars of Xanthomonas arboricola Represent Widespread Epidemic Clones Distinct from Poorly Pathogenic Strains, as Revealed by Multilocus Sequence Typing

“…Interspecies recombination at atpD and rpoD loci was also detected in our data set for strains belonging to pathovars guizotiae and populi, respectively. The occurrence of interspecies homologous recombination at housekeeping gene loci was previously revealed in other bacterial species (78,79). Our data support a predominant role of intra-and interspecies recombination in shaping the genetic diversity of X. arboricola.…”

Species diversity, spatial distribution, and virulence associated genes of culturable vibrios in a brackish coastal Mediterranean environment

“…Terai et al (1991) hypothesize that the tdh ancestor gene would probably originate in V. hollisae and spread to some strain of o ther environmental Vi brionaceae, as V. parahaemolyticus, V. cholerae non-O1, and V. mimicus, probably via an insertion sequence. Moreover, according to Theethakaew et al (2013), the presence of different haemolysin gene profiles within V. parahaemolyticus, accounts for horizontal gene transfers events involving both the tdh and trh encoding genes. The presence of tdh and trh negative isolates within V. parahaemolyticus is actually quite common in the environment (Robert-Pillot et al 2004;Ceccarelli et al 2013) and have been also found in clinical samples (Haley et al 2014).…”