Generality
Helicobacter pylori is the name of a GRAM-negative bacterium, 2.5-5 μm long, able to colonize the stomach mucosa; the consequent infection establishes a local inflammatory picture, which can progress towards important pathologies such as chronic gastritis, non-ulcerative dyspepsia, peptic ulcer and stomach cancer.
Although the intraluminal environment of the stomach is such as to prevent the growth of the vast majority of microbial forms, Helicobacter pylori has developed several survival strategies, to the point of being able to infect more than 50% of the world population.
Fortunately, in most cases (around 80-85%) the infection manifests itself in asymptomatic or modest amounts.
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The history of Helicobacter pylori begins in 1983 thanks to Robin Warren and Barry Marshall, the two Australian doctors who were the first to demonstrate the presence of a spiral-shaped microorganism in biopsy specimens of gastric mucosa. Until that time, the medical community was absolutely convinced that it was not possible for the stomach to take root and develop bacteria, given the strongly acidic pH and the marked digestive enzymatic activities that characterize it.
Thanks to numerous studies on Helicobacter pylori, various mechanisms have been identified through which this germ can survive in such a hostile environment:
- the Helicobacter pylori is a microaerophilic bacterium: as such it is able to grow without problems even in a little oxygenated atmosphere;
- the helicobacter pylori has a spiral shape and is equipped with flagella at the polar end: thanks to these characteristics it is able to produce a "corkscrew" movement which, together with the production of mucinase, allows it to penetrate the mucus barrier that protects the gastric mucosa;
- Helicobacter pylori is equipped with adhesins and glycocalyx, which, if necessary, allow it to adhere to the gastric epithelium, remaining immune to peristaltic movements and to the continuous replacement of the mucous layer that protects the gastric walls;
- Helicobacter pylori shows a marked urease activity: once it has penetrated into the mucous layer, the bacterium finds an ideal habitat, able to repair it both from the action of the acid present in the stomach and from that of the antibodies. The bacterium's chances of survival are further increased by its ability to produce urease, an enzyme that breaks down urea into carbon dioxide and ammonia. Due to its basicity, this substance neutralizes the acid produced in the stomach, ensuring an ecological niche with pH suitable for the growth of helicobacter pylori. In fact, ammonia (NH 3 ) has the ability to capture the H + protons supplied by water (H + + OH-), with formation on one side of ammonium ions (NH4 +) and on the other of bicarbonate (HCO3- thanks to the combination of the hydroxide OH- of water with carbon dioxide CO 2 ).
- Enzymes such as catalase and superoxide dismutase, which protect bacteria against the bactericidal effect of immune cells, also contribute to the survival of infectious colonies. Moreover, in hostile conditions, the Helicobacter pylori takes the coccoid form, which gives it properties of resistance both in the stomach and in the environment.
Epidemiology
Given its great ability to nest and survive in the gastric environment, Helicobacter pylori is responsible for a particularly widespread infection, so that it affects about half of the world population. As far as the industrialized countries are concerned, it is estimated that the incidence coincides approximately with the decade of age of belonging. Thus, for example, in the age group between 40 and 50, the incidence can be estimated at around 40-50% of the population. This age-proportional trend is still lost after 60-65 years, probably due to the greater diffusion of atrophic gastritis, which in affected subjects generates an unfavorable environment for the micro-organism.
The progressively increasing incidence of incidence up to the age of 60 can be explained considering that older individuals are more likely to have lived in more unfavorable sanitary conditions than in later generations ("cohort effect"). Not surprisingly, the prevalence is higher in developing countries and it is no coincidence that Helicobacter pylori infection is contracted almost exclusively in childhood, especially under ten years; for this reason, thanks to the improved hygienic and socio-economic conditions, today's children have a probability of being infected much lower than a few decades ago.
As we will see in the following paragraphs, although the prevalence of infection is around 30-65% of adults and 5-15% of children, in the great majority of cases it remains completely asymptomatic. In the absence of an effective antimicrobial therapy, after being contracted, the Helicobacter pylori infection can still persist even for the entire course of life.
