Characterization of class 1 integrons-mediated antibiotic resistance among calf pathogenic Escherichia coli

Escherichia coli isolates from calf diarrhea cases (n = 22) in the Beijing surrounding region in China were characterized for disease serotype, virulence factors, antimicrobial susceptibility pattern and class 1 integrons. 59% (n = 13) of the isolates were positive for the int I1 gene. The presence and genetic content of class 1 integrons in 13 E. coli isolates were examined by PCR and sequencing. Sequencing analysis revealed six gene cassettes, which encoded resistance to trimethoprim (dfrA1, dfrA17), aminoglycosides (aadB, aadA1 and aadA5) and chloramphenicol (cmlA). The gene cassette arrays dfrA1-orf (45%) and aadB-orf-cmlA (32%) were most prevalent among these isolates. These data revealed the high prevalence of class 1 integrons among calf pathogenic E. coli isolates in the Beijing surrounding region in China, which may provide important and useful surveillance information reflecting specific antibiotic selective pressure.