| Summary: | Abstract Background Individuals can be infected with multiple strains of Helicobacter pylori. However, the differences among co-infecting strains have not been well analyzed yet. This study aimed to investigate whether the virulence factors and antibiotic resistance patterns of H. pylori differ between strains isolated from different locations of the stomach in the same patient. Methods H. pylori isolates were obtained from the antrum and body of the stomach. Genetic differences were examined by random amplified polymorphic DNA (RAPD) fingerprinting. Antibiotic resistance was assessed using the agar dilution method. Virulence factors were identified by polymerase chain reaction and DNA sequencing. Results Among 80 patients, co-infection by two H. pylori strains was detected in 10 patients. Among the 10 pairs of H. pylori strains, differences in antibiotic resistance patterns were detected in 7 pairs (clarithromycin, 1 patient; quinolone, 3 patients; metronidazole, 4 patients) and differences in virulence factors were detected in 5 pairs. The cagA virulence gene was detected in all 10 patients, and 2 patients had H. pylori strains with different EPIYA motifs. Differences in vacA genotypes were detected in 4 patients. Conclusions Co-infection by two H. pylori strains was confirmed by RAPD fingerprinting. Frequently, two H. pylori strains obtained from a single host differed in their virulence factors and antibiotic resistance patterns. Co-infection by multiple H. pylori strains could undermine the success of eradication therapy and should be considered when interpreting the results of antimicrobial susceptibility tests.
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