Helicobacter pylori gene silencing in vivo demonstrates urease is essential for chronic infection

PLoS Pathog. 2017 Jun 23;13(6):e1006464. doi: 10.1371/journal.ppat.1006464. eCollection 2017 Jun.

Abstract

Helicobacter pylori infection causes chronic active gastritis that after many years of infection can develop into peptic ulceration or gastric adenocarcinoma. The bacterium is highly adapted to surviving in the gastric environment and a key adaptation is the virulence factor urease. Although widely postulated, the requirement of urease expression for persistent infection has not been elucidated experimentally as conventional urease knockout mutants are incapable of colonization. To overcome this constraint, conditional H. pylori urease mutants were constructed by adapting the tetracycline inducible expression system that enabled changing the urease phenotype of the bacteria during established infection. Through tight regulation we demonstrate that urease expression is not only required for establishing initial colonization but also for maintaining chronic infection. Furthermore, successful isolation of tet-escape mutants from a late infection time point revealed the strong selective pressure on this gastric pathogen to continuously express urease in order to maintain chronic infection. In addition to mutations in the conditional gene expression system, escape mutants were found to harbor changes in other genes including the alternative RNA polymerase sigma factor, fliA, highlighting the genetic plasticity of H. pylori to adapt to a changing niche. The tet-system described here opens up opportunities to studying genes involved in the chronic stage of H. pylori infection to gain insight into bacterial mechanisms promoting immune escape and life-long infection. Furthermore, this genetic tool also allows for a new avenue of inquiry into understanding the importance of various virulence determinants in a changing biological environment when the bacterium is put under duress.

MeSH terms

  • Animals
  • Bacterial Proteins / metabolism
  • Chronic Disease
  • Gastric Mucosa / microbiology
  • Gastritis / genetics*
  • Gastritis / microbiology
  • Gene Expression / genetics
  • Gene Silencing / physiology*
  • Helicobacter Infections / immunology*
  • Helicobacter pylori / genetics*
  • Mice
  • Stomach Neoplasms / genetics
  • Urease / metabolism*

Substances

  • Bacterial Proteins
  • Urease

Grants and funding

This work was supported by a PhD scholarship from the Natural Sciences and Engineering Research Council of Canada (NSERC, www.nserc-crsng.gc.ca), an Early Career Research Fellowship from the National Health and Medical Research Council (NHMRC, www.nhmrc.gov.au) (APP1073250) and an ECR Fellowship Support Grant from the University of Western Australia (www.uwa.edu.au) to AWD. SMW was supported by a NHMRC Early Career Research Fellowship (APP10555014) and a fellowship of the Swiss National Science Foundation (www.snf.ch PBEZP3-133260). KAS thanks the Australian Research Council for funding (www.arc.gov.au, FT100100291). The study was also supported by a NHMRC Sir McFarlane Burnett Fellowship grant (572723) to BJM, the University Western Australia, the Western Australian Government’s Department of Commerce (www.commerce.wa.gov.au) and Department of Health (www.health.wa.gov.au). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.