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Antimicrobial resistance and class 1 integron-associated gene cassettes in Salmonella enterica serovar Typhimurium isolated from pigs at slaughter and abattoir environment

Lopes, Graciela Volz, Michael, Geovana Brenner, Cardoso, Marisa, Schwarz, Stefan
Veterinary microbiology 2016 v.194 pp. 84-92
Salmonella Typhimurium, ampicillin, antibiotic resistance, chloramphenicol, genes, hybrids, plasmids, polymerase chain reaction, quinolones, replicon, serotypes, slaughter, slaughterhouses, spectinomycin, streptomycin, sulfonamides, swine, swine production, tetracyclines, trimethoprim, virulence, Brazil
Forty-five multi-resistant Salmonella enterica subsp. enterica serovar (S.) Typhimurium isolates obtained at five pig abattoirs in Southern Brazil were characterized. Their relatedness was determined by XbaI-macrorestriction analysis. Resistance genes, integrons and plasmid-mediated quinolone resistance genes (PMQR) were investigated by PCR. Amplicons for the variable part of class 1 integrons and the quinolone resistance-determining regions (QRDR) were sequenced. Plasmids were characterized by conjugation assays and replicon typing. Eighteen XbaI-macrorestriction patterns and 19 plasmid profiles were seen. Resistance to ampicillin (blaTEM), chloramphenicol (catA1 and floR), streptomycin (strA-strB), streptomycin/spectinomycin (aadA variants), sulphonamides (sul1, sul2, sul3) and tetracyclines [tet(A) and tet(B)] were commonly found. A trimethoprim resistance gene, dfrA8, was identified on a 100-kb plasmid. Single substitutions in the QRDR of GyrA but no PMQR genes were found. Twenty-five isolates carried class 1 integrons with an aadA23 gene cassette or unusual class 1 integrons with a dfrA12-orfF-aadA27 gene cassette array. Both integrons were found on large conjugative plasmids. Salmonella plasmid-located virulence genes spvR, spvA, spvB, rck and pefA were found on an IncFIB resistance plasmid. Hybrid virulence-resistance plasmids or plasmids harbouring class 1 integrons may play a role in the maintenance and dissemination of antimicrobial resistance among S. Typhimurium in this pig production system.