The human gut microbiota are critical for preserving the health status because they are required for digestion and nutrient acquisition, the development of the immune system, and energy metabolism. The gut microbial composition is greatly influenced by the colonization of the recalcitrant pathogen Helicobacter pylori (H. pylori) and the conventional antibiotic regimens that follow. H. pylori is considered to be the main microorganism in gastric carcinogenesis, and it appears to be required for the early stages of the process. However, a non-H. pylori microbiota profile is also suggested, primarily in the later stages of tumorigenesis. On the other hand, specific groups of gut microbes may produce beneficial byproducts such as short-chain fatty acids (acetate, butyrate, and propionate) that can modulate inflammation and tumorigenesis pathways. In this review, we aim to present how H. pylori influences the population of the gut microbiota to modify the host immunity and trigger the development of gastric carcinogenesis. We will also highlight the effect of the gut microbiota on immunotherapeutic approaches such as immune checkpoint blockade in cancer treatment to present a perspective for further development of innovative therapeutic paradigms to prevent the progression of H. pylori-induced stomach cancer.

BACKGROUND: Helicobacter pylori (H. pylori) has been introduced by since 1983 by Marshal and Warren to play the main role in the pathophysiology of gastritis and gastric ulcers. Almost half of the world population1 is infected by H. pylori. Current therapeutic regimen against H. pylori includes the use of a proton pump inhibitor plus two or more antibiotics. However, the efficacy of this regimen is decreasing mainly due to antibiotic resistance and side effects of medications. This fact has resulted in public interest in other therapeutic options and the role of probiotics merits special attention in this regard. OBJECTIVE: This study aims to evaluate the efficacy of honey-derived Lactobacillus rhamnosus on H. pylori-induced gastric inflammation and gastro-intestinal infection in C57BL/6 Mice. METHODS: The 24 C57BL/6 Mice were randomly divided into three groups of eight mice each. All the mice were fed with 1cc suspension containing 5*1010 CFU/ mL of ATCC43504 strains of H. pylori for 3 consecutive days, twice daily via polyethylene gavage tubes. At the end of 4th week, infection with H. pylori was confirmed with stool Ag (ELISA) and following sacrifice of one mouse from each group, histopathologic study confirmed gastritis. The groups were subjected to different therapies as stated, 1: without Bismuth (Bi), Omeprazole (Om) and L. rhamnosus prescription, 2: Bi, Om and Clarithromycin (Cl) and 3: Bi, Om plus 1cc of suspension of 109 CFU/mL of L. rhamnosus. After 2 weeks, the stool was analyzed for Ag and the mice were sacrificed for evaluation of histopathologic changes. RESULTS: Treatment with L. rhamnosus group provided Zero titer of stool Ag and was associated with improved gastric inflammation in all subjects, similar to the clarithromycin group. CONCLUSION: Honey-derived L. rhamnosus probiotics provides similar results as clarithromycin in terms of improvement of H. pylori infection and gastritis in C57BL/6 Mice model, without its cons of antibiotic resistance.

<b><i>Background and Aim:</i></b> <i>Helicobacter pylori</i> is one of the most common pathogenic bacteria in the human gut, and is also one of the most important factors that cause digestive disorders such as chronic inflammation, gastric ulcers, and even gastric cancer. Since the use of various antibiotics to treat <i>H. pylori</i> infection is associated with the development of resistance in this bacterium, the aim of this study was to determine the anti-<i>H. pylori</i> effects of <i>Lactobacillus acidophilus</i>, <i>L. plantarum</i>, and <i>L. rhamnosus</i> in the stomach tissue of C57BL/6 mice. <b><i>Materials and Methods:</i></b> In this experimental study, 70 mice in ten groups were evaluated from July to September 2017 in the microbiology laboratory of the School of Medicine, Alborz University of Medical Sciences, Karaj, Iran. After induction of <i>H. pylori</i> infection in mice with the standard strain of <i>H. pylori</i> (ATCC 43504), the infected mice were treated with drug and <i>Lactobacillus</i> species in different groups. Then, the anti-<i>H. pylori</i> effects of lactobacilli were evaluated by stool antigen test and tissue staining. <b><i>Results:</i></b> Based on ELISA results and histological findings, a reduction of inflammation was observed. The group which was only exposed to <i>L. rhamnosus</i> and the one which was exposed to all three strains of <i>Lactobacillus</i> showed the highest antimicrobial effect on <i>H. pylori</i>. <b><i>Conclusion:</i></b> According to the results of this study, probiotic bacteria including <i>L. acidophilus</i>, <i>L. plantarum</i>, and <i>L. rhamnosus</i> could be useful in the reduction of <i>H. pylori</i> infection in the mouse model.

Background and Objectives: Helicobacter pylori, is a major etiologic agent associated with gastritis. There is more evi- dence of noncoding microRNAs (miRs) dysregulation in gastrointestinal diseases, including inflammation caused by Helico- bacter pylori. Also, the classification of gastrointestinal malignancies using the miRs profile is better than the protein profile. MiRNA-155(miRNA-155) among other miRs plays an important role in control of inflammation and gastric malignancy, so it can be remarkable prognosis marker of gastric cancer in the phase of chronic gastritis. The aim of this study was to compare the expression of miRNA-155 in gastric biopsy and serum samples of adult patients with chronic gastritis. Materials and Methods: Biopsy and blood samples were collected from endoscopy candidates at Taleghani hospital, Tehran, during 2019. H. pylori infection was detected using histology, culture and molecular PCR methods. Based on cagA and vacA genotyping, the toxicity of H. pylori isolates were determined. After RNA extraction, the expression rate of miRNA-155 was evaluated by real-time polymerase chain reaction (RT-PCR) in gastric tissue and serum of adults infected by H. pylori (n = 30) compared with control group without infection (n = 20). RNU6 housekeeping miRNA were used as endogenous control and statistical analyses were performed using SPSS, ANOVA and Student’s t-test. Results: miRNA-155 expression in H. pylori infected adult patients increased significantly by 5.61 and 10.11 fold in serum and tissue respectively, compared to that observed in the control group. Evaluation of miRNA-155 expression pattern in relation to bacterial virulence factors showed that the increase in miRNA-155 expression is independent of CagA and VacA toxins. Conclusion: According to the differential expression patterns of miRNA-155 in serum samples of the infected adult patients, miRNA-155 has the potential to evaluate as chronic gastritis marker.