Occurrence, virulence factors, and antimicrobial susceptibility patterns of Vibrio spp. isolated from live oyster (Crassostrea gigas) in Korea

This study determined the incidence, virulence factors, and antimicrobial susceptibility patterns of Vibrio spp. in live oysters (Crassostrea gigas) marketed in Korea. A total of 41 Vibrio spp. isolates including 23 Vibrio alginolyticus, 11 Vibrio fluvialis and 7 Vibrio antiquarius were isolated and identified. All Vibrio spp. isolates showed DNase, amylase, lipase, phospholipase, and gelatinase activities. For slime production, caseinase and β-hemolysis isolates were positive in 68%, 78%, and 56%, respectively. PCR-based assays showed that V. alginolyticus expressed collagenase, tlh, toxR, ctxAB, and VPI virulence genes in 100%, 100%, 78%, 39%, and 48% of the isolates, respectively. All V. fluvialis strains harbored hupO gene while 64% and 55% isolates were positive for toxR and vfh. Besides, V. antiquarius strains were positive for toxR, tlh, ctxAB, and VPI virulence genes in 57%, 86%, 43%, and 43% of the isolates, respectively. Multiple Antibiotic Resistance (MAR) index calculated with disk diffusion test results revealed that 54% of the isolates were having MAR indices >0.2. Our results reveal that consumption of raw oysters may cause potential risk for public health owing to the Vibrio spp. comprising putative virulence properties and antimicrobial resistance. Practical applications: The genus Vibrio are most commonly associated with seafood-borne diseases. Oysters are one of the most preferred seafood in Korea as well as throughout the world. However, it may harbor pathogenic Vibrio spp., can cause foodborne illnesses if consumed as raw or undercooked product. In this study, the prevalence and characteristics of Vibrio spp. isolated from oysters in Korean markets was investigated. Among a total of 41 isolates presumptively identified by biochemical tests as vibrios, the incidence of three Vibrio species was confirmed by gyrB sequencing. Most of the isolates showed positive results for pathogenicity tests and virulence gene tests indicating the putative virulence of Vibrio spp. Susceptibility for 14 antimicrobials were tested using disk diffusion method. All the isolates were resistant to ampicillin while resistance to some other antimicrobials were also observed. According to these results, it is worthwhile to raise consumer awareness that consumption of oysters from markets in Korea may pose a risk of Vibrio infection.