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Antimicrobial Agents and Chemotherapy, December 1998, p. 3053-3058, Vol. 42, No. 12
0066-4804/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

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

Fabio Tosini,1 Paolo Visca,2 Ida Luzzi,2 Anna Maria Dionisi,2 Cristina Pezzella,2 Andrea Petrucca,3 and Alessandra Carattoli2,*

Laboratory of Cellular Biology1 and Laboratory of Bacteriology and Medical Mycology,2 Istituto Superiore di Sanità Rome, and Institute of Microbiology, University of Rome, "La Sapienza,"3 Rome, Italy

Received 10 March 1998/Returned for modification 7 July 1998/Accepted 9 September 1998

The presence and genetic content of integrons were investigated for 37 epidemiologically unrelated multiple-drug-resistant strains of Salmonella 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 the aadB, 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 same Salmonella isolate are examples of how mobile gene cassettes may contribute to the acquisition and dissemination of antibiotic resistance.

* Corresponding author. Mailing address: Laboratory of Bacteriology and Medical Mycology, Istituto Superiore di Sanità, V. le Regina Elena 299, 00161 Rome, Italy. Phone: 39-6-49903128. Fax: 39-6-49387112. E-mail: ALECARA{at}ISS.IT.

Antimicrobial Agents and Chemotherapy, December 1998, p. 3053-3058, Vol. 42, No. 12
0066-4804/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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