High-level clarithromycin resistance: a metabolic vulnerability exploited by bismuth in Helicobacter pylori

Background & AimsClarithromycin (CLA) resistance severely compromises the efficacy of triple therapy (TT) against Helicobacter pylori (H. pylori). Bismuth-based regimens exhibit greater efficacy against CLA-resistant H. pylori than against strains resistant to other antibiotics, suggesting a resistance-specific vulnerability rather than broad antimicrobial activity. The mechanistic basis for this selectivity, however, remains unknown. We hypothesized that high-level CLA resistance confers a metabolically targetable vulnerability that can be exploited by bismuth, and that a quantitative MIC of CLA threshold could identify this responsive subset. MethodsWe conducted a real-world retrospective analysis of 4,610 pediatric patients with H. pylori infection treated between 2019 and 2024, among whom 1,844 (40%) had complete follow-up data for eradication assessment. In parallel, we prospectively enrolled 51 patients with culture-positive isolates--the largest liquid checkerboard panel reported to date--to evaluate bismuth-CLA interactions and track treatment outcomes. Mechanistic validation included transcriptomic profiling and functional assays of iron and ATP metabolism, with iron chelation and supplementation experiments. ResultsIn the retrospective real-world cohort (n = 4,610; 1,844 with follow-up), bismuth quadruple therapy (BQT) achieved superior eradication specifically in CLA-resistant infections (93.1% vs 68.8% with TT; p = 0.017). In vitro, bismuth-CLA synergy was exclusive to resistant strains and intensified with increasing MIC of CLA. Mechanistically, bismuth triggered coordinated depletion of intracellular iron and ATP--a phenotype mimicked by iron chelation and reversed by iron supplementation. A baseline MIC of CLA [&ge;]16 g/mL robustly predicted this synergy (AUC = 0.991) and was prospectively validated in an independent patient subset: bismuth cured 96% of high-level resistant patients (MIC [&ge;] 16 g/mL) versus 0% with triple therapy (p < 0.001). ConclusionHigh-level CLA resistance defines an iron-dependent metabolic vulnerability in H. pylori that is selectively targeted by bismuth. The MIC threshold of [&ge;] 16 g/mL provides the first clinically actionable biomarker for resistance-guided therapy, transforming a marker of treatment failure into a positive predictor of bismuth response. These findings establish the mechanistic and clinical foundation for MIC-stratified eradication strategies and inform future randomized trials aimed at precision management of antibiotic-resistant H. pylori infection. Graphical abstractO_ST_ABSLeftC_ST_ABSHigh-level clarithromycin (CLA) resistance defines a distinct physiological phenotype in Helicobacter pylori, in which an elevated MIC of CLA ([&ge;] 16 {micro}g/mL) predicts poor eradication with triple therapy (TT) but favorable response to bismuth-containing quadruple therapy (BQT). MiddleMechanistically, CLA resistance is associated with upregulation of the ferric uptake regulator Fur, leading to reprogrammed iron homeostasis and an increased metabolic burden. Colloidal bismuth subcitrate (CBS) disrupts Fur-dependent iron regulation, exacerbates iron-restricted metabolic stress, and compromises cellular integrity, thereby selectively sensitizing CLA-resistant bacteria to antibiotic killing. RightTranslational implication of reframing antibiotic resistance as a therapeutic vulnerability--bismuth-based regimens function as a "key" that unlocks resistance-associated metabolic liabilities, delays resistance evolution, and improves treatment outcomes. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=113 SRC="FIGDIR/small/26351907v1_ufig1.gif" ALT="Figure 1"> View larger version (46K): org.highwire.dtl.DTLVardef@28fb58org.highwire.dtl.DTLVardef@8d5190org.highwire.dtl.DTLVardef@1e5fc9dorg.highwire.dtl.DTLVardef@2bc102_HPS_FORMAT_FIGEXP M_FIG C_FIG