JAC Advance Access published online on June 11, 2008
Journal of Antimicrobial Chemotherapy, doi:10.1093/jac/dkn233
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Original research |
Analysis and distribution of class 1 and class 2 integrons and associated gene cassettes among Escherichia coli isolates from swine, horses, cats and dogs collected in the BfT-GermVet monitoring study
Institute of Farm Animal Genetics, Friedrich-Loeffler-Institute, Höltystr. 10, 31535 Neustadt-Mariensee, Germany
Received 24 April 2008; returned 16 May 2008; revised 19 May 2008; accepted 19 May 2008
* Corresponding author. Tel: +49-5034-871-241; Fax: +49-5034-871-246; E-mail: stefan.schwarz{at}fli.bund.de
Objectives: In the BfT-GermVet monitoring study, 417 Escherichia coli isolates collected during 2004–06 in Germany from various disease conditions of pigs (n = 87), horses (n = 102) or cats/dogs (n = 228) were investigated for their susceptibility to 24 antimicrobial agents. This study dealt with the identification of integron-associated resistance genes among these isolates.
Methods: Class 1 and class 2 integrons were detected by PCR. The variable parts of the integrons were cloned and sequenced. Transformation and conjugation experiments were conducted to confirm a plasmid location of the integrons.
Results: Class 1 and/or class 2 integrons, alone or in different combinations, were detected in 79 of the 417 E. coli isolates. Four trimethoprim resistance genes (dfrA1/12/14/17), five streptomycin/spectinomycin resistance genes (aadA1/2/4/5/6), two streptothricin resistance genes (estX, sat2), one gentamicin/tobramycin/kanamycin resistance gene (aadB) and one chloramphenicol resistance gene (catB3) were detected. Seven different cassette arrangements were identified within class 1 integrons: aadA1 (21 isolates), dfrA1 + aadA1 (18 isolates), dfrA17 + aadA5 (9 isolates), dfrA12 + orfF + aadA2 (8 isolates), aadB + aadA1 (1 isolate), dfrA14 + recombined aadA6 (1 isolate) and dfrA1 + catB3 + aadA4 (1 isolate). Three different cassette arrangements in class 2 integrons, dfrA1 + sat2 + aadA1 (24 isolates), estX + sat2 + aadA1 (6 isolates) and estX + sat2 + 
aadA1 (1 isolate), were identified. The plasmid location of class 1 and/or class 2 integrons was confirmed in 37 isolates.
Conclusions: Class 1 and/or class 2 integrons carrying resistance gene cassettes were detected in 18.9% of the isolates tested. This molecular analysis complements the phenotypic susceptibility testing conducted in the BfT-GermVet monitoring study and helps to explain the persistence of resistance genes even without direct selective pressure.
Key Words: antimicrobial multiresistance , food animals , pets , companion animals , conjugation , plasmids
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