Abstract
Vibrio parahaemolyticus is an aquatic halophilic bacterium that occupies estuarine and coastal marine environments, and is a leading cause of seafood-borne food poisoning cases. To investigate the environmental reservoir and potential gene flow that occurs among V. parahaemolyticus isolates, the virulence-associated gene content and genome diversity of a collection of 133 V. parahaemolyticus isolates were analyzed. Phylogenetic analysis of housekeeping genes, and pulsed-field gel electrophoresis, demonstrated that there is genetic similarity among V. parahaemolyticus clinical and environmental isolates. Whole-genome sequencing and comparative analysis of six representative V. parahaemolyticus isolates was used to identify genes that are unique to the clinical and environmental isolates examined. Comparative genomics demonstrated an O3:K6 environmental isolate, AF91, which was cultured from sediment collected in Florida in 2006, has significant genomic similarity to the post-1995 O3:K6 isolates. However, AF91 lacks the majority of the virulence-associated genes and genomic islands associated with these highly virulent post-1995 O3:K6 genomes. These findings demonstrate that although they do not contain most of the known virulence-associated regions, some V. parahaemolyticus environmental isolates exhibit significant genetic similarity to clinical isolates. This highlights the dynamic nature of the V. parahaemolyticus genome allowing them to transition between aquatic and host-pathogen states.
Highlights
Vibrio parahaemolyticus is halophilic aquatic bacterium that is ubiquitous in coastal marine and estuarine environments
Parahaemolyticus As a measure of the virulence potential of V. parahaemolyticus clinical and environmental isolates analyzed, we detected common markers of virulence including: the ORF8 gene of the filamentous vibriophage, the hemolysins, the type III secretion systems of chromosome I (T3SS1), and chromosome II (T3SS2α and T3SS2β) (Table 1). These genes have been previously identified in association with illness-associated V. parahaemolyticus, and the hemolysins and T3SS2 were characterized for their role in pathogenesis (Kaper et al, 1984; Nishibuchi and Kaper, 1995; Nasu et al, 2000; Park et al, 2004; Lynch et al, 2005; Ono et al, 2006; Nair et al, 2007; Broberg et al, 2011; Ham and Orth, 2012; Zhang and Orth, 2013)
The ORF8 gene encoded by the filamentous vibriophage f237, which has previously been linked to the post-1995 O3:K6 pandemic clinical isolates (Nasu et al, 2000), was identified in 32% of the clinical isolates, and none of the environmental isolates in this study (Table 1)
Summary
Vibrio parahaemolyticus is halophilic aquatic bacterium that is ubiquitous in coastal marine and estuarine environments. In 1996, an increase in diarrheal illness in India associated with V. parahaemolyticus infections were attributed to the emergence of a novel genetic variant in 1995 that had the O3:K6 serotype (Okuda et al, 1997). This novel diseaseassociated O3:K6 clone rapidly disseminated worldwide and is considered to be pandemic (Vuddhakul et al, 2000; Myers et al, 2003; Quilici et al, 2005; Ottaviani et al, 2008). The hemolysins and type III secretion have been identified as a major components of the V. parahaemolyticus virulence mechanism (Park et al, 2004; Burdette et al, 2008; Caburlotto et al, 2010; Ham and Orth, 2012; Zhang and Orth, 2013), diseaseassociated isolates have been identified that do not encode the thermostable direct hemolysins (Yu et al, 2006; Bhoopong et al, 2007; Meador et al, 2007), suggesting there may be additional, as yet, uncharacterized genes contributing to V. parahaemolyticus virulence mechanisms
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