Helicobacter pylori, referred to as Hp. It was first discovered by Barry J. Marshall and J. Robin Warren that they won the 2005 Nobel Prize in Physiology or Medicine.
Morphological characteristics
Helicobacter pylori is a unipolar, multi-flagellate, blunt-end, spiral-shaped bacteria. Length 2.5 ～ 4.0μm, width 0.5 ～ 1.0μm. Gram stain negative. Motivated. On the surface of gastric mucosal epithelial cells, they are typically spiral or curved. When growing on solid medium, in addition to the typical shape, it may sometimes appear rod-shaped or spherical.
Under the electron microscope, one end of the bacterial body can extend 2 to 6 sheathed flagella. When splitting, flagella can be seen at both ends. Flagella length is about 1 to 1.5 times that of bacteria. Roughly about 30nm. The tip of the flagella is sometimes seen as a bulb, which is actually an extension of the sheath. Each flagella root can be seen with a spherical root extending into the inside of the cell wall at the top of the cell. On the inner side, there is still a region with reduced electron density. The flagellum acts as a propeller in movement and as an anchor during settlement.
Physiological and molecular biology characteristics
Helicobacter pylori is a micro-aerobic bacteria, the environmental oxygen requirements 5-8%, can not grow in the atmosphere or absolute anaerobic environment. Many solid culture media can be used as the basic culture medium for Helicobacter pylori isolation and culture. Brinell agar is used more, but it needs to be added with appropriate amount of whole blood or fetal bovine serum as a supplement to grow. Vancomycin, TMP, amphotericin B and other bacteriostatic agents are often used to prevent the growth of mixed bacteria.
Helicobacter pylori does not respond to most of the classic biochemical experiments commonly used to identify gut bacteria in clinical microbiological experiments. The seven enzyme reactions of oxidase, catalase, urease, alkaline phosphatase, r-glutamyl transpeptidase and leucine peptidase are the basis for the biochemical identification of Helicobacter pylori.
The complete gene sequence of Helicobacter pylori has been determined, and the urease gene has four open reading frames, namely UreA, UreB, UreC and UreD. The polypeptides encoded by UreA and UreB are equivalent to the two subunit structures of the urease structure. Helicobacter pylori is extremely rich in urease, containing about 15% of the bacterial protein, and its activity is equivalent to 400 times that of Proteus. Urease catalyzes the hydrolysis of urea to form an ammonia cloud to protect bacteria from high acid environment. In addition, there are VacA genes and CagA genes that encode vacuolar toxin and cytotoxin-related proteins, respectively.
Based on the expression of these two genes, the Helicobacter pylori strains are divided into two main types: type â… contains CagA and VacA genes and expresses two proteins, type â…¡ does not contain CagA genes, does not express two proteins, there are still some It is an intermediate expression type, which expresses one of the virulence factors. It is now believed that Type â… is closely related to gastric diseases.
to cultivate
The biopsy specimens of gastric mucosa used for culture should be placed in physiological saline, nutrient broth or 20% glucose, and then immediately transferred to the bacterial room for culture. If the specimen cannot be cultured within 4 hours, it should be stored at 4 degrees Celsius, but not more than 24 hours. The only way to preserve biopsy specimens for culture for a long time is to place them in -70 degrees Celsius or liquid nitrogen.
The medium for cultivating Helicobacter pylori includes non-selective and selective. Commonly used non-selective media bases are Brain Heart Infusion Agar, Columbia Agar, Tryptone Soy Agar, and Wilkins-Chalgren Agar. 7% -10% defibrinated horse blood needs to be added to the culture medium. Sheep blood, human blood, horse serum, heme chloride, starch, cholesterol or cyclodextrins can also replace horse blood. The selection medium is to add certain antibacterial drugs, such as vancomycin, pyridic acid, amphotericin B, polymyxin B, and trimethoprim (TMP) to the above medium.
Commonly used are Skirrow formula and Dent formula. The former was originally used for the cultivation of Campylobacter and can also be used for the cultivation of Helicobacter pylori. The latter is an improvement of the former, that is to replace polymyxin with cefsulodin, because a small number (about 5%) of H. pylori strains are sensitive to polymyxin. Drnt formula is vancomycin (10mg / L), cefsulodin (5mg / L), TMP (5mg / L) and amphotericin B (5mg / L). It is reported that some strains are sensitive to citric acid, so the antibiotic should be avoided in the medium as much as possible.
Helicobacter pylori infection detection method
There are many inspection methods for H. pylori infection, including direct bacterial inspection, urinary enzyme activity measurement, immunological detection, and polymerase chain reaction.
(1) Direct inspection of bacteria
It refers to taking gastric mucosa (mostly gastric antrum mucosa) through gastroscope forceps for direct smear, staining, tissue section staining and bacterial culture to detect Helicobacter pylori. Among them, gastric mucosal bacterial culture is the most reliable method for diagnosing Helicobacter pylori. It can be used as a "gold standard" for verifying other diagnostic tests, and can also be used for drug sensitivity tests to guide clinical drug selection.
(2) Urease test
Because H. pylori is the only bacterium in the human stomach that can produce large amounts of uremic enzymes, H. pylori infection can be diagnosed by detecting uremic enzymes. Uremic enzymes decompose uremic in the stomach to produce ammonia and carbon dioxide, which lowers the urea concentration and increases the ammonia concentration. Based on this principle, a variety of detection methods have been developed: â‘ Urease test of gastric biopsy; â‘¡ Breath test; â‘¢ Determination of urea or urea nitrogen in gastric juice; â‘£ 15N-urea test.
(3) Immunological testing
There are various immunological detection methods to detect H. pylori infection by measuring H. pylori antibodies in serum, including complement binding test, agglutination test, passive hemagglutination test, immunoblotting technique and enzyme combined adsorption assay (ELISA) Wait.
(4) Polymerase chain reaction technology
Helicobacter pylori is rarely detected in normal gastric mucosa (0 to 6%). The detection rate of H. pylori in patients with chronic gastritis is very high, about 50% to 80%. High, more than 90%.
(5) C-14 breath detector + breath detection pocket
Only need to blow for 5 minutes without any other discomfort. This method enables many patients with high blood pressure, heart disease and allergies to gastroscope to avoid the discomfort of doing gastroscope, which is one of the ideal detection methods at present. It is currently the gold standard in the HP medical industry. Sensitivity 95%, specificity 95% ~ 100%.
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