Abstract
Vibrio parahaemolyticus is a well-recognized pathogen of humans. To better understand the ecology of the human-pathogenic variants of this bacterium in the environment, a study on the prevalence in bivalves of pathogenic variants (tlh+ and tdh+ and/or trh+) versus a non-pathogenic one (only tlh+ as species marker for V. parahaemolyticus), was performed in two bays in Catalonia, Spain. Environmental factors that might affect dynamics of both variants of V. parahaemolyticus were taken into account. The results showed that the global prevalence of total V. parahaemolyticus found in both bays was 14.2% (207/1459). It was, however, significantly dependent on sampling point, campaign (year) and bivalve species. Pathogenic variants of V. parahaemolyticus (tdh+ and/or trh+) were detected in 3.8% of the samples (56/1459), meaning that the proportion of bivalves who contained tlh gene were contaminated by pathogenic V. parahaemolyticus strains is 27.1% (56/207). Moreover, the presence of pathogenic V. parahaemolyticus (trh+) was significantly correlated with water salinity, thus the probability of finding pathogenic V. parahaemolyticus decreased 1.45 times with every salinity unit (ppt) increased. Additionally, data showed that V. parahaemolyticus could establish close associations with Ruditapes spp. (P-value < 0.001), which could enhance the transmission of illness to human by pathogenic variants, when clams were eaten raw or slightly cooked. This study provides information on the abundance, ecology and characteristics of total and human-pathogenic V. parahaemolyticus variants associated with bivalves cultured in the Spanish Mediterranean Coast.
Highlights
Vibrio parahaemolyticus is a bacterium commonly present in marine and estuarine water worldwide (Kaneko and Colwell, 1975).The virulence of V. parahaemolyticus, among other virulence attributes, depends on the presence of a thermostable direct hemolysin (TDH, tdh gene) and/or the thermostable direct hemolysin related (TRH, trh gene; Takeda, 1982; Shirai et al, 1990; Honda and Iida, 1993; Oliver and Kaper, 2007; Ceccarelli et al, 2013; Raghunath, 2015)
During four summer surveillance campaigns, a total of 1459 bivalve mollusks (C. gigas, M. galloprovincialis, R. decussatus, and R. philippinarum) at commercial size, were collected and processed in the two shellfish production areas of Alfacs and Fangar Bays of the delta of Ebro river to assess the prevalences of V. parahaemolyticus
When prevalences of total V. parahaemolyticus were analyzed in each bay over the sampling period, it was observed that the prevalence in Alfacs Bay decreased significantly (P = 0.007) over the studied period: 2006 (16.6%), 2008 (13.5%), 2009 (8.9%), 2010 (5.2%); while, the prevalence of total V. parahaemolyticus in Fangar bay was significantly different among years (P < 0.001), but fluctuating over time: 2006 (15.0%), 2008 (31.0%), 2009 (8.1%), and 2010 (10.7%; Figure 2)
Summary
Vibrio parahaemolyticus is a bacterium commonly present in marine and estuarine water worldwide (Kaneko and Colwell, 1975).The virulence of V. parahaemolyticus, among other virulence attributes, depends on the presence of a thermostable direct hemolysin (TDH, tdh gene) and/or the thermostable direct hemolysin related (TRH, trh gene; Takeda, 1982; Shirai et al, 1990; Honda and Iida, 1993; Oliver and Kaper, 2007; Ceccarelli et al, 2013; Raghunath, 2015). Vibrio parahaemolyticus is a bacterium commonly present in marine and estuarine water worldwide (Kaneko and Colwell, 1975). Despite that the bacterium can be Prevalence of Vibrio parahaemolyticus in bivalves found naturally in seafood and taking into account that bivalves are filter feeders and accumulate environmental bacteria in their gills and digestive glands becoming potential vectors for many pathogens (Potasman et al, 2002), pathogenic isolates capable of inducing gastroenteritis in humans are rare in environmental samples (2 to 3%) or even undetectable (Nair et al, 2007; Canizalez-Roman et al, 2011; Velazquez-Roman et al, 2012; Haley et al, 2014). The scenario could worsen by climate global change which plays an important role in the dissemination of pathogenic microorganism in the marine environment (BakerAustin et al, 2013; Huehn et al, 2014; Letchumanan et al, 2014)
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