Dissemination of a new gene cluster comprising sul3 (tnp-sul3-tnp) linked to class 1 integrons with an unusual 3'CS region (qacH) among Salmonella isolates

Abstract number: 1733_13

Antunes P., Machado J., Peixe L.

Objectives: The objective of this study was to characterise the genetic background of sul3 gene, including their association to integron structures, in non-typhoid Salmonella isolates, in order to explain the dissemination of this sulfonamide resistance gene.

Methods: Forty-seven sul3-carrying Salmonella isolates from different sources (human, food products and environment) and serotypes were studied. Characterisation of class 1 integrons was done by PCR, RFLP (TaqI) and sequencing. Clonality analysis (PFGE-XbaI) and location of the sul3 gene by conjugation assays, plasmid analysis and Southern blot hibrydisation (S1-PFGE) were performed.

Results: A gene cluster comprising sul3 and transposase-like sequences (tnpA-sul3-orf1-IS26) was linked to class 1 integrons with an unusual 3'CS region (qacH). Three types of elements differing in the gene cassette array were observed: type I) 5'CS-dfrA12-orfF-aada2-cmlA1-aadA1-qacH-tnpA-sul3 (ca. 7000 bp), located in twelve MDR isolates (four serotypes corresponding to five clones) on large plasmids of different sizes (≥100 Kb, conjugation achieved in five); type II) 5'CS-dfrA12-orfF-aadA2/1-qacH-tnpA-sul3 (ca. 4500 bp), only described in the MDR S. Rissen clone on identical conjugative plasmids of ca. 70 Kb; type III) 5'CS-estX-psp-aadA2-cmlA1-aadA1-qacH-tnpA-sul3 (ca. 7300 bp), located in thirty-two MDR S. typhimurium isolates (corresponding to three clones) on high molecular weight plasmids of different sizes (between 150 and 240 Kb).

Conclusion: We describe the dissemination of sul3 associated with plasmid-borne class 1 integrons containing an unusual 3'CS site. The presence of similar sul3-integron platforms containing different gene cassettes arrays or hybrid genes suggests evolution of the genetic background by different recombinatorial events. The association with epidemic plasmids and particular MDR clones of Salmonella might contribute to the maintenance and further spread of modular antibiotic resistance elements from food animals to hospitalised humans as reported for other Salmonella genetic elements.

Session Details

Date: 31/03/2007
Time: 00:00-00:00
Session name: European Society of Clinical Microbiology and Infectious Diseases
Location: ICC, Munich, Germany
Presentation type:
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