Salmonella enterica is one of the most dangerous food-borne pathogens posing a significant global concern especially to travelers returning from developing countries. Given that chicken is the main reservoir for Salmonella, the emergence and spread of multi-drug resistant Salmonella from chicken have not been fully described in Vietnam. The present study aimed to evaluate the phenotypic and genotypic antimicrobial resistances of Salmonella from chicken carcasses. Among 104 raw chickens collected from 5 districts in Hanoi city, 65 samples were contaminated with Salmonella of which the highest contamination rate was found in Thanh Xuan. A total of 63/65 (96.9%) of Salmonella isolates were resistant to at least one antibiotic and 61/65 (93.9%) of the isolates were found to be multidrug resistant. Whole-genome sequencing was employed to analyze 4 strains with high (12_S2 and 61_S18) and low (19_S4 and 8_S1) antimicrobial resistance patterns. Genomic analysis indicated the presence of 27 genes conferring antibiotic resistance. Genotypes were highly correlated to observed phenotypes in 4 strains. Importantly, extended-spectrum β-lactamase blaCTX-M-55 and colistin resistance mcr-3 were reported in isolates of Salmonella enterica serovar Typhimurium. This is the first report showing the prevalence and genome sequences of Salmonella from chicken carcasses collected in Hanoi, Vietnam. The results represented herein provided the basis to understand the dynamics of antibiotic resistance of Salmonella in Vietnam and to spot antimicrobial resistance determinants for early diagnosis.
Salmonella enterica is one of the most dangerous foodborne pathogens listed by the World Health Organization. In this study, whole-duck samples were collected at wet markets in five districts in Hanoi, Vietnam, in October 2019 to assess their Salmonella infection rates and evaluate the susceptibility of the isolated strains to antibiotics currently used in the prophylaxis and treatment of Salmonella infection. Based on the antibiotic resistance profiles, eight multidrug resistance strains were whole-genome-sequenced, and their antibiotic resistance genes, genotypes, multi-locus sequence-based typing (MLST), virulence factors, and plasmids were analyzed. The results of the antibiotic susceptibility test indicate that phenotypic resistance to tetracycline and cefazolin was the most common (82.4%, 28/34 samples). However, all isolates were susceptible to cefoxitin and meropenem. Among the eight sequenced strains, we identified 43 genes associated with resistance to multiple classes of antibiotics such as aminoglycoside, beta-lactam, chloramphenicol, lincosamide, quinolone, and tetracycline. Notably, all strains carried the blaCTX-M-55 gene, which confers resistance to third-generation antibiotics including cefotaxime, cefoperazone, ceftizoxime, and ceftazidime, as well as resistance genes of other broad-spectrum antibiotics used in clinical treatment such as gentamicin, tetracycline, chloramphenicol, and ampicillin. Forty-three different antibiotic resistance genes were predicted to be present in the isolated Salmonella strains’ genomes. In addition, three plasmids were predicted in two strains, 43_S11 and 60_S17. The sequenced genomes also indicated that all strains carried SPI-1, SPI-2, and SPI-3. These SPIs are composed of antimicrobial resistance gene clusters and thus represent a potential threat to public health management. Taken together, this study highlights the extent of multidrug-resistant Salmonella contamination in duck meat in 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).
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