Antimicrobial activity and postantibiotic effect of flurithromycin against Helicobacter pylori strains

The minimal inhibitory concentrations (MIC) of flurithromycin on 49 clinical isolates of Helicobacter pylori was investigated. The MICs were determined using an agar dilution technique. Flurithromycin inhibited the growth of H. pylori strains with MIC50 and MIC90 values of 0.156 and 0.625 mg/l, respectively. The postantibiotic effects (PAE) were studied on ten strains, by exposure of the bacteria to flurithromycin at five and ten times MIC for 1 or 2 h. Regrowth was determined by measuring the viable counts after drug removal by a 103 dilution procedure. All PAEs increased as a function of concentration and time of exposure. The mean duration of PAEs varied between 1.5 and 6 h. These data are encouraging since macrolides play a key role in the clinical treatment of H. pylori infections, and the strong PAE caused by flurithromycin may contribute to the in vivo efficacy of this drug.