Prevalences of metronidazole- and clarithromycin-resistant Helicobacter pylori isolates in Shanghai and molecular mechanism of resistance to clarithromycin

OBJECTIVE: To investigate the prevalences of metronidazole- and clarithromycin-resistant Helicobacter pylori over the period from 1995 to 1999 in Shanghai, and the molecular mechanism of resistance to clarithromycin. METHODS: A total of 150 H. pylori strains were randomly selected from the isolates collected in 1995, 1997 and 1999, and tested for sensitivity against metronidazole and clarithromycin by using the E-test. The mechanism of resistance was studied by polymerase chain reaction (PCR)–restriction fragment length polymorphism (RFLP). RESULTS: It was found that 42% (21/50), 57% (27/50) and 70% (35/50) of the tested strains were resistant to metronidazole among the isolates collected in 1995, 1997 and 1999, respectively. In 1995, there was no strain (0/50) resistant to clarithromycin, of which the prevalence rose to 2% (1/50) in 1997, and to 10% (5/50) in 1999. The prevalences of metronidazole- and clarithromycin-resistant H. pylori in 1999 were significantly higher than those in 1995 (P < 0.05). Of nine clarithromycin-resistant H. pylori strains, eight were found to have an AG mutation at position 2144 of domain V of the 23S rRNA. CONCLUSIONS: These results suggest a significant increase in the prevalences of metronidazole- and clarithromycin-resistant H. pylori in Shanghai during the 1995–1999 period. The majority (88.8%) of clarithromycin-resistant H. pylori isolates have an A2144G mutation in domain V of the 23S rRNA.