Colloidal bismuth subcitrate impedes proton entry into Helicobacter pylori and increases the efficacy of growth‐dependent antibiotics

Abstract

Background Successful eradication of Helicobacter pylori is becoming more difficult, mainly due to emerging antibiotic resistance. Treatment regimens containing bismuth have increased efficacy, but the mechanism is unknown. H. pylori is a neutralophile adapted to survive the acidic gastric environment via acid acclimation, but demonstrates more robust growth at neutral pH. Many antibiotics used to treat H. pylori rely on bacterial growth. Aim To investigate the mechanism of increased efficacy of bismuth-containing H. pylori treatment regimens. Methods RNAseq and qPCR, urease activity in permeabilized and intact bacteria, internal pH, and membrane potential were measured with and without colloidal bismuth subcitrate (CBS). Bacterial survival was assessed with CBS and/or ampicillin. Results Genes involved with metabolism and growth were upregulated in the presence of CBS at acidic pH. Urease activity of permeabilized H. pylori at pH 7.4 and 4.5 decreased in the presence of CBS, but intact urease activity only decreased at acidic pH. The fall in cytoplasmic pH with external acidification was diminished by CBS. The increase in membrane potential in response to urea addition at acidic medium pH was unaffected by CBS. The impact of CBS and ampicillin on H. pylori survival was greater than either agent alone. Conclusions Bismuth is not acting directly on urease or the urea channel. CBS impedes proton entry into the bacteria, leading to a decrease in the expected fall in cytoplasmic pH. With cytoplasmic pH remaining within range for increased metabolic activity of a neutralophile, the efficacy of growth dependent antibiotics is augmented.

Role of bismuth in improvingHelicobacter pylorieradication with triple therapy

“…The proportion of organisms with visible bismuth increased over time and reached 100% by 24 h. While there was no change in viability during the first 8 h of incubation, a 3 log drop in viability was evident at 24 h confirming bacteriocidal activity of bismuth. The most recent in vitro study also used bismuth subcitrate and reported that bismuth impeded proton entry into the organisms potentially impairing their ability to respond to acid and enhancing the efficacy of growth-dependent antibiotics 72. One suspects that this finding might be related to the deposition of bismuth into the periplasmic space described previously 64 73…”

Eradication of Helicobacter pylori Infection

“…Older in vitro studies suggest that bismuth may work against H. pylori via deposition both on the surface of the bacteria and in the region between the cell wall and the cytoplasmic membrane, disrupting critical bacterial functions [69, 70]. More recent in vitro work suggests that bismuth impedes proton entry into the bacteria, allowing for up-regulation of growth-dependent genes and increased efficacy of growth-dependent antibiotics [71]. The downsides to bismuth-containing quadruple therapy include increased complexity of the regimens and increased side-effect potential, which may interfere with compliance.…”

Risk factors of rescue bismuth quadruple therapy failure for Helicobacter pylori eradication

“…Recently, Marcus et al . have suggested that bismuth impedes proton entry into the bacteria, leading to decrease in expected fall of cytoplasmic pH . With cytoplasmic pH remaining within range for increased metabolic activity of a neutrophil, the efficacy of growth dependent antibiotics is augmented .…”

“…have suggested that bismuth impedes proton entry into the bacteria, leading to decrease in expected fall of cytoplasmic pH . With cytoplasmic pH remaining within range for increased metabolic activity of a neutrophil, the efficacy of growth dependent antibiotics is augmented . Furthermore, increasing the dose and duration of metronidazole also improves outcomes of metronidazole‐resistant strains, demonstrating that, unlike clarithromycin and levofloxacin, in vitro metronidazole resistance is not an absolute predictor of eradication failure .…”