Helicobacter pylori Paolo Ruggiero,

Helicobacter pylori Paolo Ruggiero, Rino Rappuoli, and Giuseppe Del Giudice
20.1 Introduction
Helicobacter pyloriis a spiral-shaped, Gram-negative bacillus that has been cohabiting with humans for at least 100000 years: indeed, at present it is possible to trace hu- man migrations by studying H. pylori populations and subpopulations, thanks to pe- culiar gene sequences and distinct geographical distributions [1–3]. The first notices of bacteria in the mammalian stomach date back to the late 19th century, when spiral microorganisms were observed in the human stomach, and the idea of an association between bacteria and ulcer disease arose. In the same period, spiral bacteria were also found in dog stomachs, and their ability to infect mice was proven. During the first decades of 20th century these observations were sporadically confirmed and broadened, but the hypothesis of bacterial origin of peptic ulcer dis- ease was not generally accepted (for an historical overview onHelicobacter see [4]). At the end of 1970s a ‘curved bacillus’ was described in human gastric biopsies, in 1982 it was isolated and cultured, and subsequently its relationship with gastritis in hu- mans was proposed [5, 6]. The possibility of culturing this microorganism allowed studying and characterizing it. First named Campylobacter pyloridis,then corrected in C. pylori, in 1989 this bacterium was finally reclassified as Helicobacter pylori [7]. Since then, a number of Helicobacter species have been identified, which are specia- lized to live in the gastric mucosa or in other sites of humans or other mammalian species [8]. H. pylori represents the most important Helicobacter species for humans, since it chronically infects the gastric mucosa of more than 50% of the human population worldwide, varying with geographic region and socioeconomic conditions. The ma- jority of infections are asymptomatic; nevertheless, 15%–20% of infected individuals incur severe gastroduodenal diseases, such as gastritis, peptic ulcer, and gastric can- cer. In 1994 H. pylori was classified as a category 1 carcinogen by the World Health Organization [9]