Abstract
Pandemic Vibrio parahaemolyticus is an emerging public health concern as it has caused numerous gastroenteritis outbreaks worldwide. Currently, the absence of a global overview of the phenotypic and molecular characteristics of pandemic strains restricts our overall understanding of these strains, especially for environmental strains. To generate a global picture of the sero-prevalence and genetic diversity of pandemic V. parahaemolyticus, pandemic isolates from worldwide collections were selected and analyzed in this study. After a thorough analysis, we found that the pandemic isolates represented 49 serotypes, which are widely distributed in 22 countries across four continents (Asia, Europe, America and Africa). All of these serotypes were detected in clinical isolates but only nine in environmental isolates. O3:K6 was the most widely disseminated serotype, followed by O3:KUT, while the others were largely restricted to certain countries. The countries with the most abundant pandemic serotypes were China (26 serotypes), India (24 serotypes), Thailand (15 serotypes) and Vietnam (10 serotypes). Based on MLST analysis, 14 sequence types (STs) were identified among the pandemic strains, nine of which fell within clonal complex (CC) 3. ST3 and ST305 were the only two STs that have been reported in environmental pandemic strains. Pandemic ST3 has caused a wide range of infections in as many as 16 countries. Substantial serotypic diversity was mainly observed among isolates within pandemic ST3, including as many as 12 combinations of O/K serotypes. At the allele level, the dtdS and pntA, two loci that perfectly conserved in CC3, displayed a degree of polymorphism in some pandemic strains. In conclusion, we provide a comprehensive understanding of sero-prevalence and genetic differentiation of clinical and environmental pandemic isolates collected from around the world. Although, further studies are needed to delineate the specific mechanisms by which the pandemic strains evolve and spread, the findings in this study are helpful when seeking countermeasures to reduce the spread of V. parahaemolyticus in endemic areas.
Highlights
Vibrio parahaemolyticus, an organism with a high genetic diversity, has emerged as a pathogen causing acute gastroenteritis with a worldwide distribution
We conducted a comprehensive search of the US National Library of Medicine PubMed database and the Elsevier, Springer, and China National Knowledge Infrastructure databases for all relevant studies using combinations of the following terms: “Vibrio parahaemolyticus,” “pandemic clone,” “pandemic strains,” and “O3:K6 clone”
O3:KUT was the second most widely distributed serotype. Several serotypes, such as O1:K25, O1:KUT, and O4:K68, exhibited multi-country distributions but were mainly restricted to Southeast Asia (Table 1).The sources of environmental pandemic isolates were diverse, mainly including shellfish, oyster, clam, and shrimp, sediment and seawater samples collected in nine countries
Summary
An organism with a high genetic diversity, has emerged as a pathogen causing acute gastroenteritis with a worldwide distribution. In February 1996, the pandemic O3:K6 serotype emerged, resulting in an inexplicable increase of V. parahaemolyticus gastroenteritis in Kolkata city, India (Okuda et al, 1997) This unique serotype subsequently quickly spread into coastal regions of southern Asia (Bag et al, 1999), America (Martinez-Urtaza et al, 2004), Africa (Ansaruzzaman et al, 2005), and Europe (Martinez-Urtaza et al, 2005) and caused numerous outbreaks within a few years (Okuda et al, 1997; Chowdhury et al, 2000a; Nair et al, 2007). All of the pandemic serotypes are grouped as belonging to the “O3:K6 pandemic clone.” Through 2007, a total of 22 serotypes had been reported to belong to this clone (Nair et al, 2007)
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