JAC Advance Access published online on February 12, 2004
Journal of Antimicrobial Chemotherapy, doi:10.1093/jac/dkh097
© 2004 by The British Society for Antimicrobial Chemotherapy
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Original article
1 Department of Microbiology,
School of Medicine, Kyungpook National University, 101, Dongin-dong,
Jung-gu, Daegu, 700-422;
* Corresponding author. E-mail: dtcho{at}knu.ac.kr.
Received 23 May 2003
; revised 19 November 2003
; accepted 4 December 2003
Objectives: The association of trimethoprim-resistant dfr genes with integrons was investigated in urinary Escherichia coli isolates in Korea from
the last two decades. Methods: Of 623 E. coli isolates
from urine specimens, 421 trimethoprim-resistant isolates were studied
for dfr genes associated with integrons. Integrase
genes were amplified and the PCR products restricted using HinfI
to classify integron types. Gene cassette regions for the class
1 and class 2 integrons were amplified and sequenced. PFGE was performed
to determine the epidemiological relationship of E.
coli isolates. Results: The carriage of class 1 integrons was
found to be significantly higher in trimethoprim-resistant isolates
(69%) than in trimethoprim-susceptible isolates (19%).
Among the trimethoprim-resistant isolates, the frequency of dfr genes
associated with class 1 integrons increased sharply from 10% of
the isolates during 1980-1985 to 53% during 1996-1997
and to 46% during 2001-2002. Five different dfr cassettes--dfrA1, dfrA5, dfrA7, dfrA12 and dfrA17--were identified among the urinary E. coli isolates from the last two decades; dfrA12 was
the most prevalent during 1980-1985 and dfrA17 during
1996-1997 and 2001-2002. The majority of dfr genes
associated with class 1 integrons were conjugally transferable to
recipient E. coli strains. The E. coli isolates
that carried dfrA17 associated with class 1 integrons
were found to be phylogenetically unrelated, indicating that dfrA17 was
widely distributed in the different clones of E. coli. Conclusion: Class 1 integrons were found to
be an important genetic element of resistance to trimethoprim among
urinary E. coli in Korea, and the prevalence of dfrA17 was mainly due to the horizontal transfer
of class 1 integrons through conjugative plasmids.
Keywords: trimethoprim, E. coli, resistance,
conjugative plasmids
Prevalence of dfr genes associated
with integrons and dissemination of dfrA17 among
urinary isolates of Escherichia coli in Korea
2 Department
of Microbiology, Eulji University School of Medicine, Taejeon, 301-832,
Korea
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