Abstract
Background: Fluoroquinolone-resistant Helicobacter pylori emerged in 1995 and the resistance was due to point mutation in the gyrA gene. In this study we investigate the resistance mechanism and the antimicrobial susceptibilities of clarithromycin, metronidazole, amoxicillin, tetracycline and telithromycin against levofloxacin-resistant H. pylori in Hong Kong. Methods: One hundred and ninety-one nonduplicate H. pylori isolates were collected during 2004 and 2005, and 25 isolates with levofloxacin zone sizes less than 30 mm were selected for minimal inhibitory concentration determination by agar dilution, gyrA gene amplication and sequencing the amplified gyrA gene. Results: The prevalence of levofloxacin-resistant H. pylori was 11.5% (22/191). Among these levofloxacin-resistant strains, 7 (31.8%) and 10 (45.5%) were resistant to clarithromycin and metronidazole, respectively, 17 (77.3%) had point mutations in gyrA gene at amino acids 87, 91 and 130 and the most frequent mutation point was at position 91. Conclusions: Amoxicillin, tetracycline and telithromycin were active against levofloxacin-resistantH. pylori and levofloxacin resistance was mainly due to point mutation in the gyrA gene, especially at amino acid position 91.
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