Genetic basis for metronidazole and clarithromycin resistance in Helicobacter pylori strains isolated from patients with gastroduodenal disorders

BACKGROUND: The aim of this study was to evaluate the antimicrobial resistance and genetic basis for metronidazole (Mtz) and clarithromycin (Cla) resistance in strains of Helicobacter pylori, isolated from patients with gastroduodenal disorders. PATIENTS AND METHODS: A total of 157 H. pylori isolates (from 22 gastric cancer, 38 peptic ulcer disease, and 97 non-ulcer dyspepsia patients) were analyzed for drug susceptibility to Mtz and Cla, by gradient diffusion test (E-test, MAST). The PCR and sequence analysis of the rdxA and frxA for Mtz-resistant strains and the 23S rRNA for Cla-resistant strains were used to determine the genetic basis of drug resistance in H. pylori strains. Increased expression of TolC homologous genes (hefA) that upregulates efflux pump activity was determined in multidrug-resistant (MDR) strain of H. pylori by real-time PCR technique. RESULTS: Among 157 H. pylori isolates, 32 (20.4%) strains were resistant to at least one of the antimicrobial agents. The highest resistance rate was attributed to Mtz (n=69, 43.94%). Among the resistant strains of H. pylori, 15 cases (9.55%) were detected as MDR. Mutations in the rdxA (85.5%) and A2143G point mutations (63.1%) in the 23S rRNA were the most common cause of resistance to Mtz and Cla in strains of H. pylori, respectively. In MDR strains, the rdxA mutation and A2143G-point mutation in the 23S rRNA were the most abundant mutations responsible for drug resistance. The relative expression of hefA in MDR strains (mean 3.706) was higher than the susceptible strains (mean 1.07). CONCLUSION: Mutational inactivation and efflux pump overexpression are two mechanisms that increase the resistance to H. pylori antimicrobial agents and the rate of MDR strains. In Iran, the mutations of rdxA and frxA in Mtz-resistant strains and A2143G and A2142G of the 23S rRNA in Cla-resistant strains were significant. The screening for these mutations could help to prevent antibiotic resistance, and to determine the most effective anti-H. pylori drugs.