External Collaborations

Relatedness of H. pylori Strains across Communities

Background

H. pylori is a very diverse bacterial species, meaning that there are many different strains and many genetic differences between strains. Bacterial diversity is studied and classified by determining the order of the chemical bases that make up the bacteria’s DNA and genes, a process known as sequencing. H. pylori has about 1,500 genes, but scientists have identified the role played by only a few of them.

Scientists can tell how closely related two strains of H. pylori are by sequencing the DNA of selected genes and measuring how alike or different the sequences are. This can be done by sequencing just a few of the genes. Any given H. pylori strain is usually quite distinct from other strains that have come from unrelated persons. However, characteristic sets of DNA sequences are found in H. pylori strains from particular human ethnic groups or geographic regions.

The H. pylori genes that will be sequenced for this project include a few genes known as “virulence genes” and a few others known as “housekeeping genes”. Virulence genes are believed to affect the ability of the H. pylori strain to cause diseases like ulcers or cancer. Housekeeping genes are basic genes needed by all H. pylori strains for growth whether they cause disease or not.

Research Collaboration

Douglas Berg is collaborating with the CANHelp Working Group to sequence DNA from H. pylori strains that have already been cultured from residents of Aklavik. These strains were grown in a laboratory from the biopsies (stomach tissue samples) that were collected during endoscopy as part of the Aklavik H. pylori Project. Douglas Berg’s research team is characterizing these strains by DNA sequencing, using standard methods, to understand:

  • Characteristics of Aklavik strains that may be associated with health risks
  • The relatedness of strains within this community
  • The relatedness of these strains to those of other peoples in the world

Of particular interest will be sequences of genes that

  • Are believed to affect the bacteria’s ability to
    • Attach to the stomach lining and live inside the stomach
    • Cause serious disease while in the stomach
    • Resist treatment
  • Help detect relatedness of Aklavik strains to
    • Strains of other Aklavik residents
    • Strains of other Aboriginal peoples of the Arctic
    • Strains of other Aboriginal peoples of non-Arctic regions of the Americas

Douglas Berg and his team will focus on

  • Useful housekeeping genes
  • Known disease-causing genes (such as cagA and vacA)
  • Adhesion (“sticking”) genes (babA and sabA), which allow H. pylori to attach to the stomach lining
  • Susceptibility genes that determine resistance to metronidazole (rdxA and frxA), one of the drugs used most commonly to treat H. pylori

This collaboration will allow the community of Aklavik to be represented in research aimed at characterizing the H. pylori strains of peoples of the Americas and the world in order to better understand how strains are transmitted in communities and how characteristics of strains influence health risks.

Douglas E. Berg's CV available through the Washington University Medical School website

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