This study was undertaken to characterize the integrons present in a group of Shiga toxin–producing Escherichia coli (STEC) isolates and the ability of these integrons to transfer antibiotic resistance genes from STEC to E. coli K-12 MG1655. A total of 177 STEC isolates
were analyzed for antibiotic susceptibility and the presence of integrons. Class 1 integrons were detected in 14 STEC isolates, and a class 2 integron was identified in 1 STEC isolate. The STEC isolates positive for class 1 integrons were resistant to streptomycin (MICs > 128 μg/ml)
and sulfisoxazole (MICs > 1,024 μg/ml), and the isolate positive for the class 2 integron was resistant to streptomycin (MIC of 128 μg/ml), trimethoprim (MIC > 256 μg/ml), and streptothricin (MIC > 32 μg/ml). Results of restriction digestion and nucleotide sequencing revealed
that the cassette regions of the class 1 integrons had a uniform size of 1.1 kb and contained a nucleotide sequence identical to that of aadA1. The class 2 integron cassette region was 2.0 kb and carried nucleotide sequences homologous to those of aadA1, sat1, and dfrA1.
Results of the conjugation experiments revealed that horizontal transfers of conjugative plasmids are responsible for the dissemination of class 1 integron–mediated antibiotic resistance genes from STEC to E. coli K-12 MG1655. Antibiotic resistance traits not mediated by integrons,
such as resistance to tetracycline and oxytetracycline, were cotransferred with the integron-mediated antibiotic resistance genes. The study suggested a possible role of integron and conjugative plasmid in dissemination of genes conferring resistance to antibiotics from pathogenic to generic
E. coli cells.
Document Type: Research Article
Department of Food Science and Technology, The University of Georgia, 1109 Experiment Street, Griffin, Georgia 30223-1797, USA
Publication date: January 1, 2009
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