Helicobacter pylori isolates from proximal and distal stomach of patients never treated and already treated show genetic variability and discordant antibiotic resistance.

INTRODUCTION: The treatment failure of Helicobacter pylori (H. pylori) infection may be mainly because of antibiotic resistance and the presence of a mixed infection in the same patient. AIM: To investigate the incidence of mixed infection and discordant antibiotic resistance in patients never treated and already treated. MATERIALS AND METHODS: Susceptibility test to amoxicillin, rifabutin, tinidazole, clarithromycin, levofloxacin, and moxifloxacin was conducted on H. pylori strains culture from 76 patients never treated and 72 patients already treated unsuccessfully. DNA fingerprinting was determined on H. pylori strains harboring in the same patient with a discordant resistance to the same antibiotic. RESULTS: Forty percent of patients never treated and 53% of patients already treated showed a pangastric infection. The overall resistance to amoxicillin, clarithromycin, and tinidazole was significantly higher in patients with pangastric infection in comparison with those with the infection in the antrum (P<0.05). Discordant resistance was present in 33% of patients never treated, and 21% of patients already treated. DNA fingerprinting showed substantial differences among DNA patterns suggesting a mixed infection. CONCLUSION: Culture and susceptibility test should be performed when necessary not only in the antrum but also in the fundus of patients with H. pylori infection.