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
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 Delta 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
Kadlec, Kristina / Schwarz, Stefan: 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. 2008.