Occurrence and transmission of class 1 and 2 integrons among phenotypic highly ampicillin-resistant avian Escherichia coli isolates from Pakistan

Thirty four avian Escherichia coli isolates were collected from different cities of Punjab province, Pakistan during 2008–2009. Twenty five phenotypic highly ampicillin-resistant (MICs ≥ 256 μg/ml) avian E. coli strains were selected for the investigation of occurrence and transmission of class 1, 2 and 3 integrons and β-lactamase genes. Amoxicillin, sulfonamide, trimethoprim, enrofloxacin, pefloxacin and tetracycline were the most common phenotypic resistant among ampicillin-resistant avian E. coli strains. Integrons and β -lactamase were found 60 and 72% respectively. Class 1 and 2 integrons were found 52 and 8%, while class 3 integrons were not found in all strains. All class 1 positive strains had variable fragments associated with gene cassettes dfrA7, dfrA1 - aadA1, aadA1, aadA22 and dfrA12 - orfF - aadA2 respectively, which confer resistance to trimethoprim and streptomycin. Class 2-positive strains had similar gene cassettes array dfrA1 - sat1 - aadA1 conferring resistance to trimethoprim, streptothricin and spectinomicin/streptomycin. Integrons are frequently found in β -lactamase positive isolates and widely disseminate multidrug resistance genes but they do not play role in the spreading of β -lactamase genes. Class 1 integrons gene cassette aadA22 is reported for the first time in avian E. coli. Findings of this study may provide important and useful information reflecting specific antibiotic selective pressure in Punjab province, Pakistan.