The prevalence of trimethoprim-resistance-conferring dihydrofolate reductase genes in urinary isolates of Escherichia coli in Korea

One-hundred and twenty-two urinary isolates of Escherichia coli were studie d for trimethoprim resistance, Seventy-seven (63.1%) of the 122 isolates we re found to be resistant to trimethoprim. Of the 77 trimethoprim-resistant isolates, 75 dfr genes were detected in 72 isolates as follows: the dfrA17 gene was the most prevalent, being found in 27 isolates, followed by dfrA 1 2 in 26, dfr A1 in 15, dfrA5 in four and dfrA7 in three. Southern blot and PCR mapping analysis revealed that all of the dfrA17 dfrA12, dfrA5 and dfrA 7 genes were located on class 1 integrons. The dfrA 1 gene inserted as a ge ne cassette in class 1 integrons was found in 10 of 15 isolates, and the in tl2 gene of Tn7 was detected in two out of five isolates, In conjugation ex periments, the dfr genes inserted in class 1 integrons were transferred to a recipient E. coli in 32 (42.7%) of the 75 dfr genes, In conclusion, the d frA 17 and dfrA 12 genes were the most prevalent genes responsible for trim ethoprim resistance in urinary tract isolates of E, coli from Korea and the dfr genes inserted in integrons are more widespread than those that are no t related to gene cassettes.