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.