Genetic analysis of multidrug-resistant Salmonella enterica serovars Stanley and Typhimurium from cattle.
During 2005-2008, a longitudinal study was conducted in southern Japan to detect and characterize multidrug-resistant Salmonella enterica serovars recovered from cattle diagnostic specimens. Determination of antimicrobial resistance phenotypes and genotypes, identification of Salmonella genomic island 1 (SGI1), detection of virulence genes, plasmid analysis, conjugal transfer experiments, and sequencing of class 1 integrons were conducted. Multidrug-resistant Salmonella detected were serovars Stanley, Typhimurium, and O4:d. Salmonella Stanley isolates exhibited resistance to ampicillin, chloramphenicol, streptomycin, sulfamethoxazole, oxytetracycline, trimethoprim, and kanamycin (ACSSuT+) encoded by bla(TEM), catA, aadA2, tetA, sul1, dfrA12, and aphA1 genes, respectively. Sequencing analysis revealed that aadA2 and dfrA12 were integrated as gene cassettes within the class 1 integrons of 1.5kb size. Importantly, the isolates harboured easily transferable plasmids of ca. 210kb with the potential of transmitting resistance phenotype and genotype detected in the donor isolates. Moreover, Salmonella Typhimurium DT104 isolates with typical SGI1 were detected and presented ACSSuT+ resistance phenotype encoded by bla(PSE-1) and bla(TEM); floR; aadA1; sul1; and tetA and tetG, respectively. Salmonella Typhimurium isolates carried plasmids of variable sizes ranging from 3.5 to 100 kb with DT104 isolates harbouring plasmids of ca. 90 kb. Salmonella serovar O4:d had ACSSuT+ resistance phenotype mediated by bla(TEM), catA, aadA1, sul1, tetA, and aphA1 genes. A virulence gene invA was found in all multidrug-resistant Salmonella Typhimurium, Stanley and O4:d clinical isolates. In conclusion, this is the first report describing the occurrence of multidrug-resistant Salmonella Stanley from bovine species. The emergence of Salmonella Stanley isolates exhibiting plasmid-encoded high-level multidrug resistance is an important health concern because this new pathogenecity was associated with mortality in cattle.
Dahshan H
，Shahada F
，Chuma T
，Moriki H
，Okamoto K
... -
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Detailed structure of integrons and transposons carried by large conjugative plasmids responsible for multidrug resistance in diverse genomic types of Salmonella enterica serovar Brandenburg.
To evaluate the incidence, molecular basis and distribution among genomic types of antimicrobial drug resistance in Salmonella enterica (S.) serovar Brandenburg isolates recorded in the Principality of Asturias, Spain.
Thirty-seven S. Brandenburg isolates were tested for susceptibility to antimicrobial agents and typed by random amplified polymorphic DNA (RAPD) and pulsed-field gel electrophoresis (PFGE). PCR amplifications, together with DNA cloning and sequencing, were used to identify resistance genes, integrons and transposons and to establish the structure and physical associations between them. Conjugation experiments were applied to establish the location of the identified elements.
Twenty-one isolates were resistant to one or more unrelated drugs. Resistances to streptomycin, tetracycline, kanamycin, chloramphenicol, ampicillin and trimethoprim-sulfamethoxazole, encoded by aadA1, tet(A) or tet(B), aphA1, catA1, bla(TEM) and dfrA1-sul1-sul3, respectively, were most frequently observed. Multidrug resistance (32.4%) was mainly mediated by mobile genetic elements. These included: (i) class 1 integrons (with dfrA1-aadA1 gene cassettes in their variable region), which were part of Tn21-related transposons associated with Tn9; (ii) a Tn1721-derivative containing tet(A); (iii) a defective Tn10 that carried tet(B), and was linked to an integron; and (iv) large conjugative plasmids carrying a class 1 integron-Tn21-Tn9-like structure, together with the Tn1721- or the Tn10-related element. Two-way-RAPD and XbaI-PFGE discriminated the isolates into 15 and 12 profiles, respectively.
Complex genetic elements have apparently been responsible for the recruitment, assembly and dispersion of resistance genes among the highly diverse genomic types of S. Brandenburg, identified as causal agents of human salmonellosis in the Principality of Asturias, over recent years.
Martínez N
，Mendoza MC
，Rodríguez I
，Soto S
，Bances M
，Rodicio MR
... -
《JOURNAL OF ANTIMICROBIAL CHEMOTHERAPY》
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