Copyright ©The Author(s) 2018. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Gastroenterol. Jul 28, 2018; 24(28): 3071-3089
Published online Jul 28, 2018. doi: 10.3748/wjg.v24.i28.3071
Helicobacter pylori in human health and disease: Mechanisms for local gastric and systemic effects
Denisse Bravo, Anilei Hoare, Cristopher Soto, Manuel A Valenzuela, Andrew FG Quest
Denisse Bravo, Anilei Hoare, Cristopher Soto, Oral Microbiology Laboratory, Pathology and Oral Medicine Department, Faculty of Dentistry, Universidad de Chile, Santiago 8380492, Chile
Manuel A Valenzuela, Advanced Center for Chronic Diseases, Institute for Health-Related Research and Innovation, Faculty of Health Sciences, Universidad Central de Chile, Santiago 8380447, Chile
Andrew FG Quest, Advanced Center for Chronic Diseases, Center for Studies on Exercise, Metabolism and Cancer, Biomedical Science Institute, Faculty of Medicine, Universidad de Chile, Santiago 8380447, Chile
Author contributions: Bravo D, Hoare A, Soto C, Valenzuela MA and Quest AF contributed to this paper with conception and design of the study, literature review and analysis, drafting and critical revision and editing, and final approval of the final version; Bravo D, Hoare A and Soto C were involved in the design of Table 1 and Figure 1.
Supported by Comisión Nacional de Investigación Científica y Tecnológica-Fondos de Financiamiento de Centros de Investigación en Áreas Prioritarias, No. 15130011 (to Quest AF); Fondo Nacional de Desarrollo Científico y Tecnológico, No. 1170925 (to Quest AF) and No. 1171615 (to Valenzuela MA); Fondo para la Investigación en Odontología Universidad de Chile, No. 17/020 (to Bravo D).
Conflict-of-interest statement: No potential conflicts of interest. No financial support.
Open-Access: This article is an open-access article which was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See:
Correspondence to: Andrew FG Quest, PhD, Professor, Advanced Center for Chronic Diseases, Center for Studies on Exercise, Metabolism and Cancer, Biomedical Science Institute, Faculty of Medicine, Universidad de Chile, Av. Independencia 1027, Santiago 8380447, Chile.
Telephone: +56-2-27382015 Fax: +56-2-27382015
Received: April 10, 2018
Peer-review started: April 10, 2018
First decision: April 26, 2018
Revised: May 17, 2018
Accepted: June 27, 2018
Article in press: June 27, 2018
Published online: July 28, 2018

Helicobacter pylori (H. pylori) is present in roughly 50% of the human population worldwide and infection levels reach over 70% in developing countries. The infection has classically been associated with different gastro-intestinal diseases, but also with extra gastric diseases. Despite such associations, the bacterium frequently persists in the human host without inducing disease, and it has been suggested that H. pylori may also play a beneficial role in health. To understand how H. pylori can produce such diverse effects in the human host, several studies have focused on understanding the local and systemic effects triggered by this bacterium. One of the main mechanisms by which H. pylori is thought to damage the host is by inducing local and systemic inflammation. However, more recently, studies are beginning to focus on the effects of H. pylori and its metabolism on the gastric and intestinal microbiome. The objective of this review is to discuss how H. pylori has co-evolved with humans, how H. pylori presence is associated with positive and negative effects in human health and how inflammation and/or changes in the microbiome are associated with the observed outcomes.

Keywords: Helicobacter pylori, Co-evolution, Extra-gastric diseases, Inflammation, Microbiome

Core tip: This review focuses on discussing how Helicobacter pylori (H. pylori) has co-evolved with humans, potential mechanisms that may explain both positive and negative correlations in population-based studies between H. pylori infection and the development of several diseases, as well as how inflammation and/or changes in the microbiome might be linked to the respective outcomes. Our analysis of the literature reveals that human infection by H. pylori has a longstanding history, whereby the consequences therefore are extremely complex and not always detrimental to the human host. Thus, future research should focus on determining how potentially beneficial consequences of this interaction could be promoted all the while preventing the disease-causing effects in humans.