Restriction endonuclease analysis of 23S rRNA amplicons. (A) Digestion with BsaI; (B) digestion with BbsI. The A2144G mutation was found in lanes 5 to 9 and in lanes 11 and 12 but not in lanes 3, 4, and 10. Note that the A2143G mutation detected by digestion with BbsI was not detected in any of the strains studied. Lanes 3, 4, and 10 revealed the T2183C mutation, as assessed by DNA sequencing. Lane M, DNA size markers (indicated to the left of the gels in base pairs); lane 1, H. pylori ATCC 43504; lane 2, Escherichia coli DNA; lanes 3 to 12, clarithromycin-resistant H. pylori strains. Clarithromycin MICs are 16 (lane 3), 32 (lane 4), 32 (lane 5), 32 (lane 6), 32 (lane 7), 32 (lane 8), 16 (lane 9), 16 (lane 10), and 64 (lane 11) μg/ml.