The impact of a drastic change in selection pressure on trimethoprim resistance genes in clinical Escherichia coli isolates

Abstract number: 1733_375

Motakefi A., Sundqvist M., Kahlmeter G., Grape M.

Objectives: A rapid increase in resistance against trimethoprim (TRI) has been observed during the last ten years. The main mechanism of TRI-resistance is the integron-carried dihydrofolate reductase genes (dfr-genes). During 2 years (from Oct 1, 2004) an intervention project was carried out in the county of Kronoberg, Sweden, the TRICK study, where the use of trimethoprim and cotrimoxazole was reduced by 85%. By monitoring the effect of the intervention on the distribution of the five most common dfr-genes (dfrA1, dfrA5, dfrA7, dfrA12 and dfrA17) we describe changes in the mechanisms of resistance development and reversibility.

Methods: Before, during and after the intervention 100 consecutive clinical urinary E. coli isolates resistant to TRI were collected. Two multiplex PCR (mPCR) protocols using similar primers were developed, one conventional mPCR and one real-time mPCR respectively. The first ten PCR-products of each dfr-gene were sequenzed to validate the PCR methods. Both protocols were run on each isolate and the results were compared. The frequency of the five different dfr genes, were then determined as well as the distribution of these genes at each timepoint.

Results: The five selected dfr-genes were responsible for 86% of TRI resistance prior to and at mid-point of the intervention. dfrA1 was the most prevalent gene amongst the selected five genes. The distribution in the isolates collected prior to the intervention was; 39% dfrA1, 21% dfrA5, 2% dfrA7, 7% dfrA12 and 31% dfrA17. At mid-point only small shifts in the proportions of the five selected genes were seen 37% dfrA1, 15% dfrA5, 6% dfrA7, 2% dfrA12 and 27% dfrA17.

Conclusion: A high proportion of the isolates carried the five selected genes indicating that the selection of genes was relevant. 12 months of substantially reduced TRI consumption did not affect the distribution of dfr-genes to any significant extent. This implies that other factors than use of trimethoprim are of importance for determining the distribution of genetic elements encoding TRI resistance. The modest changes observed in the distribution of the five dfr-genes are being investigated further as are the hundred strains collected at the end of the intervention.

Session Details

Date: 31/03/2007
Time: 00:00-00:00
Session name: European Society of Clinical Microbiology and Infectious Diseases
Location: ICC, Munich, Germany
Presentation type:
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