Approximately 39.9% (63/158) of beef samples collected from retail markets in Hanoi from January to June 2009 were
Salmonella-positive. Nine
Salmonella serovars, Anatum (28.6%), Rissen (25.4%), Weltevreden (12.7%), Typhimurium (7.9%), Derby (7.9%), Lexington (7.9%), Dublin (4.6%), Newport (3.2%) and London (1.8%), were identified. Thirty-seven (58.7%) of the 63
Salmonella isolates were resistant to at least one antimicrobial tested, of which 29 (46%) isolates showed multidrug resistance (MDR). The isolates were commonly resistant to tetracycline (46.0%), sulphonamide (39.7%), ampicilline (31.7%), streptomycin (30.2%), trimethoprim (28.6%), kanamycin (28.6%) and chloramphenicol (22.2%). Fourteen (
blaTEMV, blaOXA-1, aadA1,
aadA2, sul1, tetA,
tetB, tetG, cmlA1, floR, dfrA1, dfrA12, aac (3)-IV and
aphA1-1AB) out of 22 antimicrobial resistance genes were detected by PCR from the resistant isolates. The
catA1,
Kn,
blaPSE-1 genes and plasmid-mediated quinolones resistance (PMQR) genes such as
qnrA,
qnrB,
qnrS,
qepA and
acc (6’)-ib-cr were not detected. Mutations in the
gyrA gene leading to the amino acid changes
Ser83Phe and/or
Asp87Asn were found in 6 out of the 11 quinolone-resistant isolates. The data revealed that multidrug resistant
Salmonella strains were widely distributed in north Vietnam via the food chain and might contain multiple genes specifying identical resistant phenotypes. Thus, continuous studies are necessary to clarify the mechanisms of MDR in
Salmonella and its spread in the livestock market.
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