Class 1 Integron-Borne Multiple-Antibiotic Resistance Carried by IncFI and IncL/M Plasmids in Salmonella enterica Serotype Typhimurium

Abstract

The presence and genetic content of integrons were investigated for 37 epidemiologically unrelated multiple-drug-resistant strains ofSalmonella enterica serotype Typhimurium from humans. All isolates were resistant to ampicillin, chloramphenicol, kanamycin, streptomycin, sulfonamides, and trimethoprim, as well as to tetracycline and/or nalidixic acid; 20% of them were also resistant to gentamicin and amikacin. Three different class 1 integrons (In-t1, In-t2, and In-t3) were identified by Southern blot hybridization, PCR, and DNA sequencing, and these integrons were found to carry theaadB, catB3, oxa1,aadA1a, aacA4, and aacC1 gene cassettes. Integrons In-t1 (aadB and catB3) and In-t2 (oxa1 and aadA1a) were both located on a conjugative IncFI plasmid of 140 kb. In-t3 (aacA4,aacC1, and aadAIa) was located on an IncL/M plasmid of 100 kb which was present, in association with the IncFI plasmid, in gentamicin- and amikacin-resistant isolates. Despite the extensive similarity at the level of the antibiotic resistance phenotype, integrons were not found on the prototypic IncFI plasmids carried by epidemic Salmonella strains isolated during the late 1970s. The recent appearance and the coexistence of multiple integrons on two conjugative plasmids in the sameSalmonella isolate are examples of how mobile gene cassettes may contribute to the acquisition and dissemination of antibiotic resistance.

Antibiotic resistance and class 1 integron patterns of non-typhoidal human Salmonella serotypes isolated in Hungary in 2002 and 2003

“…In some cases either the 1.0 kb or the 1.2 kb integron appeared alone, which suggests that these strains may have a partially deleted SGI1 and represent a subclone within DT 104 [25]. The 1.45 kb and 2.05 kb integrons that were described earlier by Tosini et al [26] as In-t1 and In-t2 located on conjugative IncFI plasmids were uniquely characteristic of this serotype. A 1.6 kb integron containing the dhfrI and aadA genes was detected alone in seven S. Typhimurium strains and in combination with other integrons in one strain.…”

Molecular investigation of an outbreak of multidrug-resistant Acinetobacter baumannii, with characterisation of class 1 integrons

“…The same cassette array has been described in type 1 integrons from Klebsiella oxytoca plasmid pACM1 [28], Salmonella enterica serotype Typhimurium IncF1 and IncM/L plasmids [29], Klebsiella pneumoniae (unpublished EMBL/GenBank accession no. AF282595) and E. coli plasmid p1658/97 (unpublished EMBL/GenBank accession no.…”

Antimicrobial resistant Salmonella in dairy cattle in the United States

“…Integrons, incorporated into plasmids and transposons, harbor multiple antimicrobial resistance genes and serve as a vehicle for the transmission of multiple resistance genes. Genes conferring resistance to amikacin (aacA4), ampicillin (oxa1), chloramphenicol (catB3), kanamycin (aadB), gentamicin (aadB, aaC1), streptomycin (aadA1a), sulfonamides (sulI), and trimethoprim (dhfrI) have been identified on integron-associated gene cassettes of Salmonella isolated from human and animal sources (Daly and Fanning 2000;Tosini et al 1998). Alcaine and colleagues provide an extensive review of antimicrobial resistance mechanisms of Salmonella and associated resistance genes (Alcaine et al 2007).…”