Prevalence and mechanisms of resistance to fluoroquinolones in Helicobacter pylori strains from patients living in Belgium

Background: Because of the increasing resistance of Helicobacter pylori against metronidazole and clarithromycin, alternative regimens including newer fluoroquinolones have been developed. We aimed to assess the prevalence as well as the mechanisms of this resistance in clinical isolates originating from patients living in Belgium. Methods: Minimal inhibitory concentration (MIC) values of ciprofloxacin, levofloxacin, and moxifloxacin were determined by Etest method on 488 H. pylori isolates originating from patients who underwent upper gastrointestinal endoscopy at 10 different centers. Resistant strains (MIC values > 1 mu g/ml) were evaluated for the presence of point mutations in the quinolone resistance-determining region (QRDR) of the gyrA by amplification and nucleotide sequence. Results: Eighty-two (16.8%) of the strains were found resistant to all fluoroquinolones and 70 of these were further analyzed. Homogeneous and heterogeneous resistance were observed in 55 (78.6%) and in 15 (21.4%) of the strains, respectively. QRDR sequencing revealed various mutations of the codons corresponding to Asn-87 and Asp-91 in all isolates with homogeneous resistance. However, in 12 of 15 strains displaying heterogenous resistance, mutations were only detected after subcultures of isolated colonies growing within the ellipse inhibition zone of the E-test. Amino acid substitutions in the QRDR of GyrA could not be directly related with the MIC values of the isolates. Fluoroquinolone-resistant mutants were easily selected in vitro at frequencies ranging between 10(-6) and 10(-7). Such selected mutants stably persisted after several serial passage in antibiotic-free agar. Conclusions: These results suggest that H. pylori resistance to fluoroquinolones is occurring at a high frequency in the Belgian population and that it is essentially mediated through a variety of point mutations occurring in a few loci of GyrA. As a consequence, we strongly suggest to determine the susceptibility of the infecting isolates to fluoroquinolones before administration of an anti-H. pylori regimen including these agents.