The pathogenic factors of H. pylori 1, bacteriophage dynamics and adhesion: Hp has the function of crossing the mucus layer and colonizing the epithelial part of the gastric sinus. 2, acid resistance and immune protection: Hp has resistance to low acidity in the stomach, so that the bacterium can survive in an acidic environment, and anti-neutrophil clearance, the role of: urease, heat shock protein, gastric acid secretion inhibitory protein, peroxidase, catalase, etc. 3. Damage to the gastric mucosal barrier: acts through cytotoxins, urease, mucolytic enzymes, etc. 4. Inflammatory response and immune response: After Hp infection, various inflammatory cells released by the cells are successively activated and chemotactic, migrating from the lamina propria to the epithelium, causing an inflammatory response. Cytokines, oxidative free radicals, hydrolases, and lysozyme released by inflammatory cells cause damage to the gastric mucosa. Chronic Hp infection causes T-cell and plasma cell infiltration, which stimulates the production of specific antibodies by these two cells and participates in the humoral immune response.Hp infection also induces an autoimmune response in the body. Digestive diseases due to H. pylori infection 1, H. pylori and gastritis: The incidence of chronic gastritis is high. Patients with epigastric discomfort have a detection rate of up to 80% or more, but its etiology has been unclear in the past. Since the discovery of H. pylori, studies have confirmed that Hp is the main cause of chronic gastritis. after Hp enters the stomach, there are short-term symptoms of acute gastritis, manifested as epigastric pain, nausea, vomiting and flatulence, which later mostly turn into chronic gastritis. The rate of Hp infection in patients with chronic active gastritis is over 95%. The gradual development of chronic active superficial gastritis can be transformed into chronic atrophic gastritis, followed by aggravation of atrophic gastritis and the occurrence of intestinal epithelial hyperplasia and heterogeneous hyperplasia, becoming precancerous. 2, H. pylori and peptic ulcer (PU): ulcers in the high rate of Hp positive, duodenal ulcer (DU), Hp infection rate of 80% to 100%, gastric ulcer (GU) patients, Hp infection rate of about 80%, eradication of Hp can significantly reduce the recurrence of PU. Thus, it is believed that Hp infection is an important causative factor for PU, especially DU, but whether PU can be recognized as an infectious disease is more controversial because most Hp-infected patients are asymptomatic. Most scholars believe that PU is essentially an Hp-associated disease, while the stimulation of gastric acid and pepsin is the key factor that determines the development of ulcers.? The role of Hp infection in the development of gastric cancer has received increasing attention, and the World Health Organization’s international research institute, the Working Group on Assessment of Human Carcinogenic Risk Factors, has concluded that H. pylori infection is a carcinogenic factor in humans, and the bacterium is classified as a class I carcinogen. The process of gastric mucosa carcinogenesis is considered as follows: normal gastric mucosa → chronic active gastritis → chronic atrophic gastritis → intestinal metaplasia → atypical hyperplasia → carcinoma, and Hp infection is associated with each of these steps. Gene mutations cause cancer. Although there is a lot of indirect evidence suggesting a close relationship between Hp infection and the occurrence of gastric cancer, there is a lack of convincing experiments to confirm that Hp is not the specific cause of gastric cancer, but there are other contributing factors (environment, diet, genetics, etc.) and only long-term chronic infection increases the risk of gastric cancer. The incidence of gastric adenocarcinoma is increased in those with long-term Hp infection and is thought to be related to the Cag A and Vac A genes, with a higher incidence of gastric cancer induced by Hp strains producing Cag A protein and Vac A s1/ml genotype. 4, H. pylori and liver disease: It is now believed that Hp not only affects the stomach, but also has damage to the liver. one of the most significant biological features of Hp is that it can produce urease to break down urea, forming an “ammonia cloud” around the bacteria, increasing blood ammonia, coupled with the hepatotoxic effect of Hp, can aggravate liver damage, inducing hyperammonemia and hepatic encephalopathy. Hp infection is also a factor that cannot be ignored in non-variceal rupture and bleeding, cirrhosis and peptic ulcer and active bleeding of gastric mucosa. At the same time, due to the change of intestinal flora, it is not conducive to the clearance of Hp, and the infection rate of Hp increases. There are also experts found that there is a kind of bacteria very similar to H. pylori in liver cancer tissue, and its relationship with liver cancer is yet to be further studied.? 5, Helicobacter pylori and non-ulcer dyspepsia (NUD): whether the detection rate of Hp is significantly higher in NUD, whether there is a correlation between the two, the relationship between Hp infection and clinical symptoms is difficult to determine, based on the results of the current study can not say that the eradication or removal of Hp can improve the clinical symptoms of NUD, in short, the relationship between Hp and NUD is a subject worthy of in-depth study. 6, low-grade malignant lymphoma: It is generally believed that associated with Hp-positive chronic gastritis, eradication of Hp treatment can cause 77% to 83% of gastric MALT lymphoma to subside. Thus, aggressive Hp eradication therapy is advocated. Other: Hp infection is also closely related to Barrett’s esophagus, gastroesophageal reflux disease, and functional dyspepsia. H. pylori infection can also occur in childhood, and many digestive diseases in childhood, such as chronic gastritis and peptic ulcer, are closely related to H. pylori infection and may be associated with the development of gastric cancer in adulthood. There are various methods for the diagnosis of H. pylori infection, which are divided into two main categories: direct methods and indirect methods. Direct method 1, bacterial culture: The gastric mucosa is ground up and immediately inoculated on a medium containing blood and selective antibiotics, and incubated for 3 d to 4 d under microaerobic conditions at 37°C. If spiral or curved Gram-negative bacilli are found, further positive results of urease, oxidase and hydrogen peroxide enzymatic tests are required to determine that the bacterial culture is accurate and reliable for Hp, often as a verification of other tests “gold standard”. However, it is time-consuming and requires certain conditions and techniques. In addition, it can also provide a drug sensitivity test for bacteria to guide clinical selection of drugs, especially for those who have failed treatment or live in countries and regions with high Hp drug resistance. Recently, it has been reported that Hp can also be cultured from human stool, but it needs to be obtained by centrifugation in a micro-oxygen environment and concentrating the bacteria, because at present it can only be detected in the stool of 50% of patients with Hp colonization, so further research is needed on this non-invasive method. 2, tissue section method: another direct examination method of Hp, can provide histomorphological information, because Hp settled in the submucous layer of human gastric mucus, epithelial cell surface, under normal circumstances there is no other bacteria in the area, so according to the morphological characteristics and distribution characteristics on tissue sections (between the gastric mucus and gastric lumen exists spiral bacilli-like material), can diagnose Hp infection, is a more reliable method. Histological examination is characterized by high sensitivity, the possibility of simultaneous pathological examination, and permanent preservation of data. There are many staining methods, including HE staining, Gram staining, carbonic acid complex red staining, W-S (Warthin-Starry) staining, Giemsa (Gimza) staining, etc. Gram staining, because of the low detection rate has almost been used; standard HE staining can detect Hp, but it is not a reliable method, W-S silver staining is a good technique, despite the high price and technical requirements, due to the effective detection, clinical application is more common, Giemsa staining cost less, some authors believe that this method is equal to W-S silver staining in quality. In addition to conventional histological examination, there are immunochemical and immunofluorescence methods, but they require the use of immunofluorescence microscopy and immunoantibodies, which make the examination more expensive and do not provide information beyond conventional histological findings, and thus cannot be used routinely and are mostly used in laboratory studies. 3, direct smear staining: direct examination of Hp in gastric mucus coated on slides with phase contrast microscopy. acridine orange staining, Gram staining, Giemsa staining are available. 4, PCR (polymerase reaction): PCR is another method to detect the presence of Hp, characterized by the rapid detection of Hp in fresh gastric mucus specimens, but also paraffin-embedded biopsy samples. primers for PCR are specific for all Hp strains, so it is highly specific. Compared with rapid urease, culture methods and histology, PCR is again highly sensitive. However, some hidden factors can affect this high sensitivity and specificity, such as endoscopy and biopsy forceps cleaning, sterilization is not strict leading to DNA contamination, so that the specificity is reduced, so that the sensitivity is reduced by the presence of bacteria in the gastric mucosa plaque colonization or PCR inhibitory factors. PCR can be used for the clinical diagnosis of Hp infection, epidemiological investigation, molecular genetic study of Hp. [2. Indirect examination of bacteria Using the biological properties of bacteria, especially the ability of Hp to hydrolyze urea and produce the breath test, urease test. Serology cannot be used for the diagnosis of current infections because it does not provide a basis for the current presence of bacteria, and is mainly used for screening or epidemiological investigations. For clinicians. According to the conditions of the hospital, it is important to choose the appropriate method to be used for patients, and currently the main use of combined methods of diagnosis. 5, microscopic examination of bacteria in tissue: the gastric mucosa tissue is evenly coated on a slide, Gram staining or complex red staining microscopic examination, the method is simple. Tissue section staining with Warthin-starry silver staining is the best, but time-consuming and requires certain techniques.? Indirect method 1, biopsy tissue urease test: the most simple, practical, mostly used for clinical diagnosis, mechanism: Hp has abundant urease, can decompose urease to produce ammonia, so that the test solution becomes alkaline, by Hp indicator color, because there is a commercial urease test kit supply, for gastroscopic examination.? 2, respiratory test: the patient orally administered isotope 13C and 14C labeled urea solution, if Hp infection, urea is decomposed to produce isotope-labeled CO2 exhaled from the lungs, the exhaled specimen can be collected for liquid scintillation counter or mass spectrometer to determine the amount of isotope-labeled CO2. This test has the advantages of being rapid, reliable, safe and painless. It has been used abroad as the best method to track and observe the effect of treatment. It is suitable for large-scale epidemiological investigations, and a distinctive feature of its superiority over serology is that it indicates whether there is currently Hp infection, rather than whether it has ever been infected. Nowadays, it is mainly used for the review after Hp treatment. 3. Serology: The enzyme-linked immunosorbent assay (ELISA) is the most effective. The use of more purified antigens such as urease, macromolecular cell-associated proteins, serology is particularly suitable for epidemiological investigations. Serology cannot be used for the diagnosis of current infections because it does not provide a basis for the current presence of bacteria, and is mainly used for screening or epidemiological investigations.? 4, other: polymerase chain reaction (PCR) and other molecular biology techniques have also been used for the diagnosis of Hp infection, making the sensitivity and specificity greatly improved.