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.
OBJECTIVE
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 + DeltaaadA1 (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
K
Institute of Farm Animal Genetics, Friedrich-Loeffler-Institute, Höltystr. 10, 31535 Neustadt-Mariensee, Germany.
Schwarz
Stefan
S
D000818:Animals; D001483:Base Sequence; D002415:Cats; D002876:Chromosomes, Bacterial / Q000235:genetics; D003001:Cloning, Molecular; D004269:DNA, Bacterial / Q000235:genetics; D004285:Dogs; D024881:Drug Resistance, Bacterial; D004926:Escherichia coli / Q000235:genetics* / Q000302:isolation & purification; D004927:Escherichia coli Infections / Q000382:microbiology / Q000662:veterinary*; D029968:Escherichia coli Proteins / Q000235:genetics; D023061:Gene Order; D005858:Germany; D006736:Horses; D032023:Integrons; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D013552:Swine
D004269:DNA, Bacterial; D029968:Escherichia coli Proteins