Molecular Characterization of Multidrug-Resistant Escherichia coli Isolates from Irish Cattle Farms

Abstract

ABSTRACT This study describes the genotypic characteristics of a collection of 100 multidrug-resistant (MDR) Escherichia coli strains recovered from cattle and the farm environment in Ireland in 2007. The most prevalent antimicrobial resistance identified was to streptomycin (100%), followed by tetracycline (99%), sulfonamides (98%), ampicillin (82%), and neomycin (62%). Resistance was mediated predominantly by strA-strB (92%), tetA (67%), sul2 (90%), bla TEM (79%), and aphA1 (63%) gene markers, respectively. Twenty-seven isolates harbored a class 1 integrase ( intI1 ), while qacE Δ 1 and sul1 markers were identified in 25 and 26 isolates, respectively. The variable regions of these integrons contained aminoglycoside, trimethoprim, and β-lactam resistance determinants ( aadA12 , aadB - aadA1 , bla OXA-30 - aadA1 , dfrA1 - aadA1 , dfrA7 ). Class 2 integrons were identified less frequently (4%) and contained the gene cassette array dfrA1-sat1-aadA1 . Resistance to ampicillin, neomycin, streptomycin, sulfonamide, and tetracycline was associated with transferable high-molecular-weight plasmids, as demonstrated by conjugation assays. A panel of virulence markers was screened for by PCR, and genes identified included vt1 , K5 in 2 isolates, papC in 10 isolates, and PAI IV 536 in 37 isolates. MDR commensal E. coli isolates from Irish cattle displayed considerable diversity with respect to the genes identified. Our findings highlight the importance of the commensal microflora of food-producing animals as a reservoir of transferable MDR.