Background:Genotypic analysis has been performed in Helicobacter pylori strains isolated before and after antibiotic therapy from patients for whom no eradication of the microbes could be achieved.Material/Methods:The Helicobacter pylori strains were isolated from 10 patients with duodenal ulcer, who were treated by the triple therapy (Controloc with amoxicillin and metronidazole). Biopsies of gastric mucosa were inoculated on the Columbia agar with antibiotics and on the medium without antibiotics. The cultures were kept in microaerophilic conditions at 37°C for 4 to 10 days. Genotype analysis was performed using PCR-based RAPD fingerprinting. The sensitivity of the strains to metronidazole, clarithromycin, amoxicillin and tetracycline was tested using E-tests.Results:In five patients, identical strains of the bacteria were noted both before and after the therapy while distinct patterns of pre- and post-treatment isolates were found in three patients. One patient demonstrated identical strains before and after the therapy but upon later control testing was found to be infected with a genotypically distinct strain. In 2 patients (a married couple) the infection was caused by genotypically distinct strains. A high proportion (46%) of metronidazole-resistant strains was detected.Conclusions:Therapeutic failures in treatment of Helicobacter pylori infections may either be the result of ineffective eradication of the strain from the stomach or of a re-infection. When applying treatment with antibiotics, high frequency of metronidazole resistance should be taken into account.

Keywords: Anti-Bacterial Agents, DNA Fingerprinting, DNA, Bacterial - analysis, Drug Resistance, Bacterial, Drug Therapy, Combination - pharmacology, Drug Therapy, Combination - therapeutic use, Duodenal Ulcer - drug therapy, Duodenal Ulcer - microbiology, Helicobacter Infections - drug therapy, Helicobacter Infections - microbiology, Helicobacter pylori - drug effects, Helicobacter pylori - genetics, Helicobacter pylori - isolation & purification, Microbial Sensitivity Tests, Random Amplified Polymorphic DNA Technique