Detection of antimicrobial resistance determinants in vibrio parahaemolyticus isolated from cultivated oysters and estuarine waters

In this study, we aimed to detect antimicrobial resistance determinants and virulence factor genes in V. parahaemolyticus isolates from cultivated oysters and estuarine waters in southern Thailand. A total of 594 V. parahaemolyticus isolates were collected from pooled oysters (n=361) and estuarine waters (n=233). The samples were collected monthly between March 2016 and February 2017 from Thap Put district, Phang Nga province in southern Thailand. Confirmation of V. parahaemolyticus was carried out by PCR assay detecting species-specific (tlh) gene and the presence of virulence genes (tdh and trh). Antimicrobial susceptibility test was performed in eight antimicrobials, and the occurrence of resistance genes was investigated. All isolates were detected for the presence of SXT elements and class 1, 2, and 3 integrons. The results showed that all presumptive V. parahaemolyticus isolates (n=594) were positive to species-specific (tlh) gene. Four isolates (0.7%) from pooled oysters (n=2) and estuarine waters (n=2) were positive to tdh. None of the trh-positive isolates were observed. In this study, 34% of the isolates were resistant to at least one antimicrobial agent and 5.1% of the isolates were multidrug-resistant (MDR). Most of the isolates were resistant to erythromycin (54.2%), followed by sulfamethoxazole (34.7%), trimethoprim (28.0%), and ampicillin (11.1%), respectively. Only 0.8% and 0.5% of the isolates were resistant to streptomycin and tetracycline, respectively, and chloramphenicol and ciprofloxacin resistance were not observed in all isolates. Among the tested antimicrobials, the prevalence of tetracycline resistance in estuarine waters was significantly higher than oyster (P < 0.05). The most frequent resistance pattern was ERY (21.0%) and the most common MDR phenotype was ERY-SUL-AMP (1.9%). The most commonly found AMR genes were qnr (77.8%) and strB (27.4%), followed by tetA (22.1%), dfr18 (19.5%), ermB (15.2%), and sul2 (14.8%), respectively. However, dfrA1 (7.4%) and blaTEM (0.8%) genes were rarely found AMR genes in this study. The occurrence of qnr and dfr18 genes were significantly different between oysters and estuarine water samples (P < 0.05). None of the isolates were possessed SXT integrase gene (intSXT) and class 1, 2, and 3 integrons. Our results highlighted the need for improving good sanitary practices and consumption of adequate cooked oysters to promote seafood safety for consumption and to reduce the risk of seafood-borne illnesses and antimicrobial resistance infection.