Study on Class 1 integrons in multidrug-resistant isolates of Escherichia coli

Objective To analyze the prevalence and molecular characterization of Class 1 integrons in multidrug-resistant Escherichia coli isolates. Methods Class 1 integrons were detected by PCR from the total DNA in 81 multidrug-resistant E. coli isolates. The RFLP analysis was carried out for amplicons of Class 1 integrons with identical size. The purified amplicons of Class 1 integrons were sequenced. The type and order of gene cassettes in integrons were analyzed by searching GenBank. Results Class 1 integrons were identified from total DNA in 48 (59.3%) isolates. The size of Class 1 integrons ranged from about 600 bp to 3 000 bp. Each of the 48 isolates had 1 or 2 Class 1 integrons. Class 1 integrons indistinguishable with respect to size had identical restriction patterns. The predominant gene cassettes included dfr17 (encoding resistance to trimethoprim) and aadA5 (encoding resistance to streptomycin and spectinomycin). The main order of inserted gene cassettes was dfr17-aadA5. Conclusions Class 1 integrons are widespread in isolates of multidrug-resistant E. coli. Integrons are important molecular mechanism in the development of multidrug resistance.