The Role Of Class I Integron In Escherichia Coli Antibiotic Resistance

Objective To investigate the antibiotic resistance, the presence of class 1 integrons and order of gene cassetes in clinical isolates of Escherichia coli. To analyze the relationship between gene cassetes and resistance phenotype. To analyze the relationship between class 1 integrons and multidrug-resistant Escherichia coli. To illuminate the molecular mechanism of integrons and gene cassetes in mediation and dissemination of antibiotic resistance.Methods The identification ofbacteria,detection of ESBLs and susceptibility to 22 antibiotics were performed in 114 Escherichia coli isolates by Vitek 2 (BioMerieux). Four other antibiotics were determined by the disk diffusion assay.Class 1 integrase(IntI1) was detected by PCR with plasmid DNA.IntI1-positive strains were further amplified for the region of antibiotics resistance genes. The purified amplicons of class 1 integrons were sequenced. We tried to find out the content and order of gene cassetes in integrons by searching in GenBank.Results Over 50% of the isolates were resistant to 12 antibiotics. Antibiotics with high resistance rate included Ampicillin(100%), Trimethoprim-sulfamethoxazole, Ceftriaxone(60%),Gentamicin(60%) and so on. Forty-six isolates(40.4%) produced ESBLs.Eighty (70.2%) isolates were multidrug resistant(resistance to over 3 antibiotics). Sixty-two strains were positive for intI gene.IntI-positive strains were further amplified for the region of antibiotics resistance genes. Among sixty-two strains, fifty- eight were positive.The size of class 1 integrons ranged from 600bp to 3500bp. Each isolate had one or two class 1 integrons. Three isolates(2.6%) had two class 1 integrons. Class 1 integrons indistinguishable with respect to size had identical restriction patterns. It was supposed that they might have the same sequences. The predominant gene cassetes included dfr17(encoding resistance to trimethoprim) and aadA5(encoding resistance to streptomycin and spectinomycin). The main order of inserted gene cassettes was dfr17-aadA5. The major isolates carrying dfr were resistant to sulfamethoxazole/trimethoprim, Most isolates carrying aadA were not susceptible to streptomycin.Conclusion Nowadays the situation of antibiotic resistance is severe in E coli clinical isolates. It is indicated that class 1 integrons might be widespread in clinical Escherichia coli. and gene cassetes in integron could be greatly related with old antibiotics such as trimethoprim and old aminoglycoside compounds. As a whole, the isolates carrying gene cassete correspond to their resistance phenotype. Integrons mediated antibiotic resistance. Genotyping is suggestive of horizontal intraspecies transfer of integrons.