Strains and virulence genes of Salmonella with multidrug resistance isolated from chicken carcasses (Hanoi, Vietnam)

Salmonella enterica is one of dangerous food-borne pathogens listed by the World Health Organization (WHO). In Vietnam, poultry is one of the most widely eaten meats and is reported as a common source of S. enterica contamination. The aim of this study was to examine multi-resistant Salmonella strains, to identify susceptibility to antibiotics by using 15 different types of medications and to perform sequencing to analyze antibiotic resistance genes, genotypes, multi-locus sequence-based typing (MLST), and plasmids. The result of the antibiotic susceptibility test indicated that phenotypic resistance to 9-11 types of antimicrobials was confirmed in all strains. Among 06 sequenced strains, we identified 43 genes associated with antibiotic resistance: strains carrying a range of genes that are associated with aminoglycoside resistance (aac(3), aac(6), ant(3), aph(3), aph(6), aadA); all strains carried blaCTX-M-55 or blaCTX-M-65 gene, which were resistant to the 3rd generation antibiotics; there were also frequently observed sul1, sul2, sul3, tet (A), qnrS1, floR, dfrA14 or dfrA27 genes in sequenced isolates. Besides, the genome sequencing also indicated that all strains carried pathogenicity islands SPI 1, SPI 2, and SPI 3 thereby creating many potential triggers of the disease. Additionally, some carried C63PI, SPI 9, SPI 13, SPI 14, and plus some plasmids such as Col156, IncHI2, IncHI2A, IncFIB, Col (MGD2).