Incidence, genetic diversity, and antimicrobial resistance profiles of in seafood in Bangkok and eastern Thailand.

BACKGROUND

Emergence of pandemic 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-pandemic had 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 of in seafood samples purchased in Bangkok and collected in eastern Thailand and characterized isolates. Potential virulence genes, VPaI-7, T3SS2, and biofilm were examined. Antimicrobial resistance (AMR) profiles and AMR genes (ARGs) were determined.

METHODS

was 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-pandemic and 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. characterization was done by multilocus sequence typing (MLST). A phylogenomic tree was built from nucleotide sequences by UBCG2.0 and RAxML softwares.

RESULTS

All 50 isolates including 21 pathogenic and 29 non-pathogenic strains from 190 samples had the 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 36 isolates 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 including (100%, 36/36), (83%, 30/36), (42%, 15/36), (6%, 2/36), (3%, 1/36), and (3%, 1/36). Phylogenomic and MLST analyses classified 36 isolates into 5 clades, with 12 known and 13 novel sequence types (STs), suggesting high genetic variation among the isolates.

CONCLUSIONS

Although none strains isolated from seafood samples purchased in Bangkok and collected in eastern Thailand were pandemic strains, around one third of isolates were MDR strains. The presence of resistance genes of the first-line antibiotics for infection raises a major concern for clinical treatment outcome since these resistance genes could be highly expressed under suitable circumstances.