Studies on the development and stability of resistance of Helicobacter pylori to metronidazole and clarithromycin

Thirty-one strains of Helicobacter pylori, susceptible to metronidazole and clarithromycin, were isolated from 31 biopsy samples from patients with va rious gastric pathologies. We investigated the possibility of selecting res istant strains and the stability of resistance by exposing isolates to incr easing subinhibitory concentrations of metronidazole and clarithromycin usi ng 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 clarithrom ycin. 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.