title: Integron-mediated antibiotic resistance in Shiga toxin-producing Escherichia coli.
abstract: 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 microg/ml) and sulfisoxazole (MICs > 1,024 microg/ml), and the isolate positive for the class 2 integron was resistant to streptomycin (MIC of 128 microg/ml), trimethoprim (MIC > 256 microg/ml), and streptothricin (MIC > 32 microg/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.
authors.affiliation: Department of Food Science and Technology, The University of Georgia, 1109 Experiment Street, Griffin, Georgia 30223-1797, USA.
authors.forename: Supakana
authors.initials: S
authors.lastname: Nagachinta
authors.forename: Jinru
authors.initials: J
authors.lastname: Chen
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001483:Base Sequence; D002417:Cattle; D015169:Colony Count, Microbial; D003227:Conjugation, Genetic; D004305:Dose-Response Relationship, Drug; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D048168:Escherichia coli K12 / Q000187:drug effects* / Q000235:genetics*; D022761:Gene Transfer, Horizontal; D005798:Genes, Bacterial; D006801:Humans; D032023:Integrons; D008826:Microbial Sensitivity Tests; D008970:Molecular Weight; D054323:Shiga-Toxigenic Escherichia coli / Q000187:drug effects* / Q000235:genetics*
chemical_list: D000900:Anti-Bacterial Agents