pylori and humans: an ancient relationship
Helicobacters inhabit the gastrointestinal tract of many mammals and birds, which often possess their own unique gastric Helicobacter species. These species are mostly host specific (ref. S1; available online with this article; doi: 10.1172/JCI38605DS1), implying coevolution of the bacteria with their hosts. By comparing nucleotide sequences of different strains and measuring maximal in vivo mutation rates, it is possible to calculate the minimal time that H. pylori and its host have shared a common ancestor (4). Genetic diversity among H. pylori strains decreases with distance from East Africa, just like genetic diversity decreases among humans (Figure 1) (5). Taken together these data show that H. pylori has coevolved with humans, at least since their joint exodus from Africa 60,000 years ago and likely throughout their evolution.