title: 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. Helicobacter 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.
  
  
  OBJECTIVE
  To investigate the mechanism of increased efficacy of bismuth-containing H. pylori treatment regimens.
  
  
  METHODS
  RNAseq and qPCR, urease activity in permeabilised 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 permeabilised H. pylori at pH 7.4 and 4.5 decreased in the presence of CBS, but intact urease activity decreased only 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. Colloidal bismuth subcitrate 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.
authors.affiliation: Department of Pediatrics, DGSOM at UCLA, Los Angeles, CA, USA.|VA GLAHS, Los Angeles, CA, USA.
authors.forename: E A
authors.initials: EA
authors.lastname: Marcus
authors.affiliation: VA GLAHS, Los Angeles, CA, USA.|Department of Physiology, DGSOM at UCLA, Los Angeles, CA, USA.|Department of Medicine, DGSOM at UCLA, Los Angeles, CA, USA.
authors.forename: G
authors.initials: G
authors.lastname: Sachs
authors.affiliation: VA GLAHS, Los Angeles, CA, USA.|Department of Physiology, DGSOM at UCLA, Los Angeles, CA, USA.
authors.forename: D R
authors.initials: DR
authors.lastname: Scott
mesh_terms: D000863:Antacids / Q000008:administration & dosage / Q000494:pharmacology; D000900:Anti-Bacterial Agents / Q000008:administration & dosage / Q000627:therapeutic use*; D003102:Colloids; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects; D016481:Helicobacter Infections / Q000188:drug therapy* / Q000378:metabolism / Q000382:microbiology; D016480:Helicobacter pylori / Q000187:drug effects / Q000235:genetics / Q000254:growth & development*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D017136:Ion Transport / Q000187:drug effects* / Q000235:genetics; D008826:Microbial Sensitivity Tests; D050296:Microbial Viability / Q000187:drug effects; D009942:Organometallic Compounds / Q000008:administration & dosage / Q000494:pharmacology*; D011522:Protons
chemical_list: D000863:Antacids; D000900:Anti-Bacterial Agents; D003102:Colloids; D009942:Organometallic Compounds; D011522:Protons; C002791:bismuth tripotassium dicitrate