Helicobacter pylori’s Unconventional Role in Health and Disease

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Helicobacter pylori’s Unconventional Role in Health and Disease

Marion S. Dorer, Sarah Talarico, Nina R. Salama*

Division of Human Biology, Fred Hutchinson Cancer Research Center,
Seattle, Washington, United States of America

Abstract

The discovery of a bacterium, Helicobacter pylori, that is resident in
the human stomach and causes chronic disease (peptic ulcer and gastric
cancer) was radical on many levels. Whereas the mouth and the colon were
both known to host a large number of microorganisms, collectively
referred to as the microbiome, the stomach was thought to be a virtual
Sahara desert for microbes because of its high acidity. We now know that
H. pylori is one of many species of bacteria that live in the stomach,
although H. pylori seems to dominate this community. H. pylori does not
behave as a classical bacterial pathogen: disease is not solely mediated
by production of toxins, although certain H. pylori genes, including
those that encode exotoxins, increase the risk of disease development.
Instead, disease seems to result from a complex interaction between the
bacterium, the host, and the environment. Furthermore, H. pylori was the
first bacterium observed to behave as a carcinogen. The innate and
adaptive immune defenses of the host, combined with factors in the
environment of the stomach, apparently drive a continuously high rate of
genomic variation in H. pylori. Studies of this genetic diversity in
strains isolated from various locations across the globe show that H.
pylori has coevolved with humans throughout our history. This long
association has given rise not only to disease, but also to possible
protective effects, particularly with respect to diseases of the
esophagus. Given this complex relationship with human health,
eradication of H. pylori in nonsymptomatic individuals may not be the
best course of action. The story of H. pylori teaches us to look more
deeply at our resident microbiome and the complexity of its
interactions, both in this complex population and within our own
tissues, to gain a better understanding of health and disease.

Citation: Dorer MS, Talarico S, Salama NR (2009) Helicobacter pylori’s
Unconventional Role in Health and Disease. PLoS Pathog 5(10): e1000544.
doi:10.1371/journal.ppat.1000544

Editor: Marianne Manchester, The Scripps Research Institute, United
States of America

Published: October 26, 2009

Copyright: © 2009 Dorer et al. This is an open-access article
distributed under the terms of the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any
medium, provided the original author and source are credited.