Characterization of aminoglycoside resistance genes and class 1 integrons in porcine and bovine gentamicin-resistant Escherichia coli

A total of 78 gentamicin-resistant Escherichia coli strains from swine (27) and cattle (51) were characterized by phenotypic resistance, presence of s elected aminoglycoside resistance genes, class 1 integrons and gene cassett es, and pulsed-field gel electrophoresis, Gentamicin resistance was mainly encoded by the ant(2")-I gene that was found in 76% of all the strains inve stigated, whereas the aac(3)-IIa gene was found in 14%, The ant(2")-I gene was predominant in strains from cattle, whereas the porcine strains contain ed both ant(2")-I, aac(3)-IIa, and the aac(3)-IVa genes. The pulsed-field g el electrophoresis (PFGE) investigation indicated a close clonal relationsh ip in half of the bovine strains whereas the remaining E, coli were unrelat ed. Among the E, coli investigated, 20% contained class 1 integrons, Genes encoding resistance to trimethoprim (dhfrI, dhfrIb, and dhfrVII), gentamici n, tobramycin, and kanamycin (ant(2")-Ia streptomycin and spectinomycin (an t(3")-Ia) and streptothricin (sat1) were identified as gene cassettes. The most prevalent gene cassettes were ant(3")-Ia (11 isolates) and the dhfrI ( nine isolates).