Long-term Monitoring and Assessment of Pathogenic Vibrio species for Seafood Safety Management

Abstract

Many outbreaks of Vibrio species such as V. parahaemolyticus, V. vulnificus, and V. cholerae that have occurred throughout the world have been associated with the consumption of raw or undercooked seafood, including oysters, which are important vehicles for the transmission of the pathogen. Reducing outbreaks caused by the consumption of raw or undercooked bivalves contaminated with pathogenic Vibrio species requires clarification of its distribution and virulence in aquatic environments. The seasonal and spatial variation of pathogenic Vibrio species, such as V. parahaemolyticus, V. vulnificus, and V. cholerae were investigated in seawater and in bivalves off the Gyeongnam coast of Korea, which is an important area for shellfish production, during the period 2013-2016. V. parahaemolyticus, V. vulnificus, and V. cholerae were detected in 12.1%, 5.2%, and 0.9% of seawater samples, respectively. V. parahaemolyticus, V. vulnificus, and V. cholerae were detected in 21.9%, 7.1%, and 0.0% of shellfish samples, respectively. The Vibrio spp. in seawater and bivalve samples were detected at high levels during the summer to early autumn; however, the levels were low during the winter. V. vulnificus is detected in shellfish during the production period of raw oysters due to the increase in seawater temperature in winter. Relatively high detection rates of the strains were also found in the sea area that was continually exposed to inland wastewater. Long-term monitoring is necessary to understand the appearance of V. parahaemolyticus caused by climate change and to reduce the occurrence of food poisoning. V. parahaemolyticus is also one of the most common causes of seafood-borne illnesses in Korea. The seafood-borne outbreaks associated with V. parahaemolyticus increased during the high temperatures of summer in Korea, especially between August and September. The occurrence of V. parahaemolyticus in both seawater and bivalve shellfish was also high in summer, especially in August, July, and September. The strain was detected at very low levels during winter to early spring because of low water temperatures on the Korean coast. However, due to the influence of climate change, the seawater temperature rises even in winter, and V. parahaemolyticus is detected in shellfish. These results indicate that the occurrence of V. parahaemolyticus on the Korean coast was dependent on season correlated with water temperature, which is also the largest factor in contributing to the food-borne outbreaks associated with it. The detection rates for V. parahaemolyticus between seawater and shellfish samples were highly correlated, and the strains in shellfish were significantly higher than those in seawater during the survey period. In addition, below 6% of isolates from seawater and shellfish samples were for the trh toxic gene, and a few strains (1.7%) only from shellfish were positive for the tdh gene. V. parahaemolyticus isolates from seawater and bivalve shellfish samples, high resistance to AM, CZ, and S was observed. All the V. parahaemolyticus isolates from seawater and bivalve shellfish samples, 75.8% and 36.7% exhibited resistance to at three or more antimicrobials. A MAR value of more than 0.2 occurred in 27.6% of the isolates from seawater and 2.0% of the isolates from bivalves. These results suggest that some sea areas in this study were likely exposed to antimicrobial contaminated sources. Therefore, these results indicate that intensive and continuous monitoring is needed to reveal the relationships between the occurrence and presence of virulence genes in Vibrio species from marine samples off the Korean coast, and to reduce the human health risk arising from the consumption of infected seafood.