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Antimicrobial Agents and Chemotherapy, June 2002, p. 1714-1722, Vol. 46, No. 6
0066-4804/02/$04.00+0     DOI: 10.1128/AAC.46.6.1714-1722.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Characterization of Variant Salmonella Genomic Island 1 Multidrug Resistance Regions from Serovars Typhimurium DT104 and Agona

David Boyd,1 Axel Cloeckaert,2 Elisabeth Chaslus-Dancla,2 and Michael R. Mulvey1*

National Microbiology Laboratory, Health Canada, Winnipeg, Manitoba, Canada R3E 3R2,1 Unité de Pathologie Aviaire et Parasitologie, Institut National de la Recherche Agronomique, 37380 Nouzilly, France2

Received 3 October 2001/ Returned for modification 14 December 2001/ Accepted 7 March 2002

Strains of multidrug-resistant Salmonella enterica serovar Typhimurium DT104 (DT104) and S. enterica serovar Agona (Agona) have been found to harbor Salmonella genomic island 1 (SGI1), a 43-kb genomic region that contains many of the drug resistance genes. Such strains are resistant to ampicillin (pse-1), chloramphenicol/florfenicol (floR), streptomycin/spectinomycin (aadA2), sulfonamides (sul1), and tetracycline [tet(G)] (commonly called the ACSSuT phenotype). All five resistance genes are found in a 13-kb multidrug resistance (MDR) region consisting of an unusual class I integron structure related to In4. We examined DT104 and Agona strains that exhibited other resistance phenotypes to determine if the resistance genes were associated with variant SGI1 MDR regions. All strains were found to harbor variant SGI1-like elements by using a combination of Southern hybridization, PCR mapping, and sequencing. Variant SGI1-like elements were found with MDR regions consisting of (i) an integron consisting of the SGI1 MDR region with the addition of a region containing a putative transposase gene (orf513) and dfrA10 located between duplicated qacE{Delta}1/sulI genes (SGI1-A; ACSSuTTm); (ii) an integron with either an aadA2 (SSu) or a pse-1 (ASu) cassette (SGI1-C and SGI1-B, respectively); (iii) an integron consisting of the SGI1-C MDR region plus an orf513/dfrA10 region as in SGI1-A (SGI1-D; ASSuTm; ampicillin resistance due to a TEM ß-lactamase); and (iv) an integron related to that in SGI1 but which contains a 10-kb inversion between two copies of IS6100, one which is inserted in floR (SGI1-E; ASSuT). We hypothesize that the MDR of SGI1 is subject to recombinational events that lead to the various resistance phenotypes in the Salmonella strains in which it is found.

* Corresponding author. Mailing address: Nosocomial Infections, National Microbiology Laboratory, Health Canada, 1015 Arlington St., Winnipeg, Manitoba, Canada R3E 3R2. Phone: (204) 789-2133. Fax: (204) 789-5020. E-mail: Michael_Mulvey{at}hc-sc.gc.ca.

Antimicrobial Agents and Chemotherapy, June 2002, p. 1714-1722, Vol. 46, No. 6
0066-4804/02/$04.00+0     DOI: 10.1128/AAC.46.6.1714-1722.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.



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