JCM Accepts, published online ahead of print on 3 January 2008

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J. Clin. Microbiol. doi:10.1128/JCM.01597-07
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Diagnostic accuracy of a class 1 integron PCR method in detection of antibiotic resistance in Salmonella isolated from swine production systems

Sangeeta Rao, Carol W. Maddox, Patricia Hoien-Dalen, Sara Lanka, and Ronald M. Weigel^*

Department of Pathobiology, University of Illinois, Urbana, IL, Veterinary Diagnostic Laboratory, University of Illinois, Urbana, IL

^* To whom correspondence should be addressed. Email: weigel{at}uiuc.edu.

The diagnostic accuracy of an integron PCR method (Int-PCR) for detecting Class1 integrons (sizes: 1000, 1200, and 1600 bp) in the identification of antibiotic resistant Salmonella was evaluated using 730 Salmonella isolates from pen floor samples collected from 4 swine production systems in Illinois. Three integron groupings were detected – 1000 bp only, 1600 bp only, and both 1000 and 1200 bp integrons. Presence of any of the three Class1 integron groupings was associated with 4-drug resistance (Streptomycin, Spectinomycin, Sulfizoxazole, Tetracycline: St-Sp-Su-Tet). In addition, presence of both the 1000 and 1200 bp integrons added resistance to Ampicillin (Amp) and Chloramphenicol (C) and the 1600 bp integron added resistance to Gentamicin (Gen) and Kanamycin (Kan). DNA sequencing of integrons confirmed the presence of the aminoglycoside adenyl transferase (aadA) gene conferring St-Sp resistance in the 1000 bp integron, the beta-lactamase gene conferring Amp resistance in the 1200 bp integron, and the aadA and aadB genes conferring St-Sp-Gen-Kan resistance in the 1600 bp integron. The 1600 bp integron appears to have the 1000 bp intergron as its core, with additional genetic material conferring additional antibiotic resistance. Diagnostic accuracy of the Int-PCR in detecting resistance to individual antibiotics was limited by the presence of phenotypic resistance in isolates without integrons. However, the Int-PCR had high diagnostic accuracy (sensitivity, specificity) in detecting multi-drug resistance: (0.98, 0.92) for St-Sp-Su-Tet, (0.95, 1.0) for Amp-C-St-Sp-Su-Tet, (1.0, 0.99) for Gen-Kan-St-Sp-Su-Tet. Thus, the Int-PCR can be a valuable in epidemiologic surveys as a screening tool for detection of multi-drug resistant Salmonella.