Distribution of Vibrio species isolated from bivalves and bivalve culture environments along the Gyeongnam coast in Korea: Virulence and antimicrobial resistance of Vibrio parahaemolyticus isolates

Vibrio species, including Vibrio parahaemolyticus, V. vulnificus, and V. cholerae, are common pathogens causing seafood-borne illnesses worldwide. In 2017, we monitored the distributions of pathogenic Vibrio strains in seawater and bivalves collected along the Gyeongnam coast in Korea, a major source of bivalve shellfish, particularly oysters, as well as products of the raw seafood industry. In addition, we determined the features of virulence and antibiotic resistance in V. parahaemolyticus isolates. Among these pathogenic Vibrio strains, V. parahaemolyticus was present at the highest level in both seawater samples (23.1%) and bivalves (39.4%). Importantly, V. parahaemolyticus were detected at high levels (>75%) in oysters during the summer and frequently present during the oyster-harvesting season, ranging from 12.5% to 50.0%. All strains positive for the virulence genes were isolated from oysters, which are commonly consumed raw in many countries, and the oyster growing water. More than 90.0% of V. parahaemolyticus isolates were susceptible to 16 of the 23 antimicrobials tested, which are effective against V. parahaemolyticus illness. More than half of the isolates were resistant to at least three antimicrobials; in particular, three antibiotics (ampicillin, cefazolin, and streptomycin) should be excluded as treatment options for V. parahaemolyticus infections due to the higher resistance of the isolates. The consumption of raw seafood, including oysters, is common in Korea; therefore, to ensure seafood safety, continuous monitoring of Vibrio strains, as well as their virulence and antimicrobial resistance, is necessary in marine food sources.