Role of Helicobacter pylori and Other Environmental Factors in the Development of Gastric Dysbiosis

Abstract

Microbiomes are defined as complex microbial communities, which are mainly composed of bacteria, fungi, and viruses residing in diverse regions of the human body. The human stomach consists of a unique and heterogeneous habitat of microbial communities owing to its anatomical and functional characteristics, that allow the optimal growth of characteristic bacteria in this environment. Gastric dysbiosis, which is defined as compositional and functional alterations of the gastric microbiota, can be induced by multiple environmental factors, such as age, diet, multiple antibiotic therapies, proton pump inhibitor abuse, H. pylori status, among others. Although H. pylori colonization has been reported across the world, chronic H. pylori infection may lead to serious consequences; therefore, the infection must be treated. Multiple antibiotic therapy improvements are not always successful because of the lack of adherence to the prescribed antibiotic treatment. However, the abuse of eradication treatments can generate gastric dysbiotic states. Dysbiosis of the gastric microenvironment induces microbial resilience, due to the loss of relevant commensal bacteria and simultaneous colonization by other pathobiont bacteria, which can generate metabolic and physiological changes or even initiate and develop other gastric disorders by non-H. pylori bacteria. This systematic review opens a discussion on the effects of multiple environmental factors on gastric microbial communities.

Keywords: Helicobacter pylori; dysbiosis; eradication therapy; gastric microbiota; non-Helicobacter pylori bacteria; probiotics.

Figure 1

PRISMA flow diagram for the identification and selection of articles on the effects of H. pylori, non-H. pylori bacteria, and multiple environmental factors on the gastric microbiota of patients and healthy subjects [9].

Figure 2

Schematic of the gastric microbial composition and alterations generated by multiple environmental factors. (A) Indicates a schematic of a healthy gastric microbiota. A healthy microbiota is defined as the coexistence of microbial communities, such as pathogenic and symbiotic bacteria with no harmful consequences. Nevertheless, dysbiotic communities can be generated due to several environmental factors, especially by Helicobacter pylori chronic infection, which can be diagnosed through histopathological analysis and differential staining techniques; (B) Giemsa stain, 100×. Arrow highlight H. pylori in biopsy; (C) H&E stain, 40×; (D) anti-Hp stain, 100×. The presence of dysbiotic communities in the gastric microenvironment usually favours the continuous loss of bacterial diversity; (E) increasing infections caused by pathobionts and the growth of antibiotic-resistant gene bacteria. Histological damage can also be observed, caused by environmental factors, that is, the abuse of PPIs (F).

Figure 3

Histopathological alterations generated by Helicobacter pylori chronic infection. (A), near-normal antral mucosa is shown (H&E 10×). (B) illustrates a case of non-atrophic gastritis; increased mononuclear infiltrate with preserved antral architecture can be observed (H&E 10×). Loss of glands and increased connective tissue can be seen in (C), representing a case of atrophic gastritis (H&E 20×). (D) Goblet cells (arrow) are present in the foveolar epithelium which correspond to an initial lesion of intestinal metaplasia (H&E 40×). (E) Hyperchromatic nuclei with loss of its polarity corresponding to dysplasia in a gastric gland, are marked with a black arrow; complete distortion of a gland with cell proliferation and loss of its basal membrane are shown with a (*) marked arrow in a case of gastric adenocarcinoma (H&E 20×). (F) Mucosal distortion of the gastric antrum, with dilated and irregular glands, is observed from a patient treated with proton pump inhibitors (H&E 10×).