Studies on the Development and Stability of Resistance ofHelicobacter pylorito Metronidazole and Clarithromycin

Thirty-one strains of Helicobacter pylori, susceptible to metronidazole and clarithromycin, were isolated from 31 biopsy samples from patients with various gastric pathologies. We investigated the possibility of selecting resistant strains and the stability of resistance by exposing isolates to increasing subinhibitory concentrations of metronidazole and clarithromycin using a serial passages technique. Resistance to metronidazole was obtained in 100% of the isolates, while 32.2% displayed resistance to clarithromycin. Resistance to metronidazole was stable in 93.5% (29 of 31) of the isolates, whereas 100% (10 of 10) of the strains were stably resistant to clarithromycin. The stability of the resistance that occurred after three passages on medium containing the two drugs was statistically significant (P <0.001). Thus, the technique of serial passages in vitro could be useful as a first screening in selecting drugs for use in therapeutic protocols for clinical trials.