Characterization of Multidrug-Resistant Escherichia coli Isolates from Animals Presenting at a University Veterinary Hospital

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Applied and Environmental Microbiology, Oct. 2011, p. 7104–7112.


In this study, we examined molecular mechanisms associated with multidrug resistance (MDR) in a collection of Escherichia coli isolates recovered from hospitalized animals in Ireland. PCR and DNA sequencing were used to identify genes associated with resistance. Class 1 integrons were prevalent (94.6%) and contained gene cassettes recognized previously and implicated mainly in resistance to aminoglycosides, -lactams, and trimethoprim (aadA1, dfrA1-aadA1, dfrA17-aadA5, dfrA12-orfF-aadA2, blaOXA-30-aadA1, aacC1-orf1-orf2-aadA1, dfr7). Class 2 integrons (13.5%) contained the dfrA1-sat1-aadA1 gene array. The most frequently occurring phenotypes included resistance to ampicillin (97.3%), chloramphenicol (75.4%), florfenicol (40.5%), gentamicin (54%), neomycin (43.2%), streptomycin (97.3%), sulfonamide (98.6%), and tetracycline (100%). The associated resistance determinants detected included blaTEM, cat, floR, aadB, aphA1, strA-strB, sul2, and tet(B), respectively. The blaCTX-M-2 gene, encoding an extended-spectrum -lactamase (ESL), and blaCMY-2, encoding an AmpC-like enzyme, were identified in 8 and 18 isolates, respectively. The mobility of the resistance genes was demonstrated using conjugation assays with a representative selection of isolates. High-molecular-weight plasmids were found to be responsible for resistance to multiple antimicrobial compounds. The study demonstrated that animal-associated commensal E. coli isolates possess a diverse repertoire of transferable genetic determinants. Emergence of ESLs and AmpC-like enzymes is particularly significant. To our knowledge, the blaCTX-M-2 gene has not previously been reported in Ireland.


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