Molecular analysis of ciprofloxacin resistance and clonal relatedness of clinical Escherichia coli isolates from haematology patients receiving ciprofloxacin prophylaxis.

OBJECTIVES Widespread use of fluoroquinolones has led to increased levels of resistance in clinical isolates of Escherichia coli. We investigated the evolution of ciprofloxacin susceptibility and molecular epidemiology of clinical E. coli isolates in haematology patients receiving ciprofloxacin prophylaxis on the population and individual patient level. METHODS From August 2006 through December 2007 we collected all E. coli isolates (n = 404) from surveillance and infection-site cultures from 169 haematology patients receiving ciprofloxacin prophylaxis. Analysis of the gyrase A (gyrA) gene was performed by denaturing gradient gel electrophoresis (DGGE) in 364 isolates and clonal relatedness was determined by the single-enzyme amplified fragment length polymorphism (seAFLP) technique in 162 isolates. One hundred of these isolates were also subjected to qnrA analysis. RESULTS The average number of samples per patient was 2.4 (maximum 20) and 122 (30%) of 404 E. coli isolates were resistant to ciprofloxacin. In 124 patients only ciprofloxacin-susceptible strains were detected. DGGE revealed 11 different gyrA sequence patterns and, based on AFLP analysis, there was evidence of selection of ciprofloxacin-resistant strains under antibiotic pressure, as well as the occurrence of genetically indistinguishable ciprofloxacin-resistant and -susceptible E. coli isolates within one patient. Clonal dissemination of ciprofloxacin-resistant E. coli was observed, but did not predominate. CONCLUSIONS The genetic evolution of clinical E. coli isolates in haematology patients receiving ciprofloxacin prophylaxis is characterized by selection of ciprofloxacin-resistant strains. However, we did find evidence for de novo resistance mutation in ciprofloxacin-susceptible E. coli in individual patients under selective pressure.