[Helicobacter pylori--friend or foe?].

Helicobacter pylori (H. pylori) is the bacterium that causes the most common infection in the world. Epidemiological studies show that over 50% of the population is infected, there are areas where virtually the entire population present the infection since childhood. Although the stomach seems to be a "hostile" environment for the development of microorganisms due to the acid pH not fit for life, it may be infected; the first spiral organisms were described at this level as early as 1874. These microorganisms were isolated by Waren and Marshall in 1982 and named Campylobacter pyloridis. In 1989 Goodwin renamed the bacterium Helicobacter pylori. Helicobacter pylori is thus a bacterium which "manages" to survive in gastric acid environment producing an infection which, untreated, is likely to persist the entire life. This feature explains the high rate in the spread of the infection. The infection manifests itself in different ways, depending on the pathogenic strain and the host response, the majority of those infected being asymptomatic or paucysymptomatic. The great achievement of Warren and Marshall,who were rewarded with a Nobel prize in 2005, was to demonstrate that H. pylori can lead to gastric cancer, the bacteria being categorized as an oncogene agent. The anti H. pylori "campaign" was only a step away... and yet, the bacterium has been living in the stomach for centuries. We will try to list the pros and cons of H. pylori infection, when and how the infection should be treated, clearly indicating groups of patients in which eradication is absolutely mandatory. Key words: