'In vitro' development of metronidazole, erythromycin, amoxicillin and gentamicin resistance in Helicobacter pylori

Serial passage of 37 Helicobacter pylori clinical isolates on increasing concentrations of metronidazole rapidly produced five strains with MICs up to 512 fold higher than those for the original strains. For these five metronidazole-resistant strains the MICs of erythromycin, gentamicin and amoxicillin were unchanged. When they were submitted to the same technique for these last antimicrobial agents, only one strain developed high level resistance to erythromycin and gentamicin having MIC values respectively up to 32 and 64-fold increased. Finally, no amoxicillin-resistant Helicobacter pylori could be obtained.