BackgroundEmergence ofVibrio parahaemolyticuspandemic strain O3:K6 was first documented in 1996. Since then it has been accounted for large outbreaks of diarrhea globally. In Thailand, prior studies on pandemic and non-pandemicV. parahaemolyticushad mostly been done in the south. The incidence and molecular characterization of pandemic and non-pandemic strains in other parts of Thailand have not been fully characterized. This study examined the incidence ofV. parahaemolyticusin seafood samples purchased in Bangkok and collected in eastern Thailand and characterizedV. parahaemolyticusisolates. Potential virulence genes, VPaI-7, T3SS2, and biofilm were examined. Antimicrobial resistance (AMR) profiles and AMR genes (ARGs) were determined.MethodsV. parahaemolyticuswas isolated from 190 marketed and farmed seafood samples by a culture method and confirmed by polymerase chain reaction (PCR). The incidence of pandemic and non-pandemicV. parahaemolyticusand VPaI-7, T3SS2, and biofilm genes was examined by PCR. AMR profiles were verified by a broth microdilution technique. The presence of ARGs was verified by genome analysis.V. parahaemolyticuscharacterization was done by multilocus sequence typing (MLST). A phylogenomic tree was built from nucleotide sequences by UBCG2.0 and RAxML softwares.ResultsAll 50V. parahaemolyticusisolates including 21 pathogenic and 29 non-pathogenic strains from 190 samples had thetoxRS/old sequence, indicating non-pandemic strains. All isolates had biofilm genes (VP0950, VP0952, and VP0962). None carried T3SS2 genes (VP1346 and VP1367), while VPaI-7 gene (VP1321) was seen in two isolates. Antimicrobial susceptibility profiles obtained from 36V. parahaemolyticusisolates revealed high frequency of resistance to colistin (100%, 36/36) and ampicillin (83%, 30/36), but susceptibility to amoxicillin/clavulanic acid and piperacillin/tazobactam (100%, 36/36). Multidrug resistance (MDR) was seen in 11 isolates (31%, 11/36). Genome analysis revealed ARGs includingblaCARB(100%, 36/36),tet(34)(83%, 30/36),tet(35)(42%, 15/36),qnrC(6%, 2/36),dfrA6(3%, 1/36), andblaCTX-M-55(3%, 1/36). Phylogenomic and MLST analyses classified 36V. parahaemolyticusisolates into 5 clades, with 12 known and 13 novel sequence types (STs), suggesting high genetic variation among the isolates.ConclusionsAlthough noneV. parahaemolyticusstrains isolated from seafood samples purchased in Bangkok and collected in eastern Thailand were pandemic strains, around one third of isolates were MDRV. parahaemolyticusstrains. The presence of resistance genes of the first-line antibiotics forV. parahaemolyticusinfection raises a major concern for clinical treatment outcome since these resistance genes could be highly expressed under suitable circumstances.