Metronidazole-resistant Helicobacter pylori isolates without rdxA mutations obtained from Iranian dyspeptic patients

Abstract

Antibiotic resistance is now accepted as an inevitable factor in Helicobacter pylori treatment failure, so a survey on the antibiotic susceptibility profile of H. pylori is welcomed. In addition, the main molecular mechanism of antibiotic resistance in H. pylori is not fully determined, particularly for metronidazole. Our single-centre study was designed to evaluate the local antibiotic resistance profile of H. pylori strains recovered from individuals with dyspepsia. Gastric biopsy specimens from 200 individuals underwent bacterial culture for H. pylori, and bacterial identification was confirmed by positive reports from biochemical and genotypic universal protocols. Antibiotic susceptibility tests were performed on the 73 isolates obtained, by both disc diffusion and E-test methods. DNA extraction was carried out on single colonies of H. pylori confirmed by biochemical tests, then PCR was used to amplify the rdxA and 23srRNA genes. Metronidazole and clarithromycin resistance phenotypes were checked to detect possible mutations at rdxA and 23SrRNA genes. Successful bacterial culture was reported for 73 of the 200 patients (27 male (36%) and 46 female (63%) with an age range from 25 to 80 years (mean 54 years)). None of the patients reported pre-treatment. Among the 73 biochemically and genotypically confirmed H. pylori isolates in this analysis, antibiotic resistance rates were 45% (33/73) for metronidazole and 23% (17/73) for clarithromycin. Additionally, ten H. pylori isolates were multidrug resistant (13%). According to the antibiogram analysis, 13/17 (76%) had the A2142G mutation, although 3/17 (17%) samples also showed A2143G. None of the resistant isolates were carrying the A2142C and A2144G mutations. Moreover, none of the metronidazole-resistant strains showed any of the point mutations. Identification of H. pylori isolates without the rdxA mutation reveals the need for an urgent investigation to select an effective antibiotic before drug prescription by gastroenterologists. Keywords: Antibiotic resistance, clarithromycin, E-test, Helicobacter pylori, metronidazole, mutation