A wide diversity of bacterial species colonise the human gastrointestinal tract, with over 1000 different species of bacteria to be found throughout. However, very few of these species are found in the stomach, with the majority of species colonising the large intestine and colon . The stomach is a harsh environment for bacteria to live in, due to acidic gastric juices and proteolytic enzymes . Gastric juices have a typical pH range of 2.0 to 6.0. This often highly acidic pH is important in preventing colonisation of the stomach by bacteria . However, some bacteria have adapted to overcome this, and have mechanisms that help them survive and thrive in the stomach. One such bacteria is Helicobacter pylori.
Helicobacter…show more content… pylori has been ingested by the host, the bacteria enter the stomach through the oesophagus. The stomach is made up of three distinct regions: the fundus, corpus, and antrum. Gastric epithelial cells are lined with a thick mucus layer. The pH in the mucosa is less acidic than in the lumen of the stomach . The three regions of the stomach differ greatly in cell composition and pH. H. pylori colonise the mucus layers of the antrum and corpus, where the pH is less acidic than in the fundus. H. pylori is a flagellated bacteria, with its polar flagella allowing it to swim through the lumen to colonise the microenvironment of the stomach’s mucus layer, an essential step in the successful invasion of the bacteria . H. pylori must act fast in attaching itself to the mucus layer, as it can only survive a pH of 2.0 in the lumen for around 30 minutes, and the bacteria are rendered immotile after just a few minutes . Motility is essential for successful colonisation of the stomach, as the bacteria need to be motile to reach the mucus layer, where the pH conditions are less…show more content… pylori uses urease, an enzyme, to help protect itself during short exposures to the low pH of the gastric acid in the lumen. Urease catalysis the hydrolysis of urea derived from the host to produce ammonia and CO2 . H. pylori excretes the ammonia into its surrounding. The excreted ammonia reacts with the hydrochloric acid in the gastric juices of the lumen to neutralise it, providing a protective neutral pH microenvironment around the bacteria . This protects them from the acid pH of the lumen during a short exposure, after which they need to seek enter a less acidic environment, the mucosa. Chemotaxis is important for surviving the stomach, and H. pylori possess several chemoreceptors that they utilise in colonising the stomach . They are used to sense low pH concentrations, and nutrient concentrations. This aids the bacteria in finding its way to the epithelium. Low pH environments are characteristic of the protective mucus layer of the epithelial cells. H. pylori can sense the presence of sodium bicarbonate, thought to be indicative of a more neutral pH, like in the mucus layer . It can also sense nutrient such as arginine, which is an essential amino acid for H. pylori. Both of these substances are excreted into the stomach by cells in the epithelial layer. Positive movement by bacteria towards these substances lead H. pylori to the mucus layer, their ideal microenvironment in the stomach