Adaptive mutation and cocolonization during Helicobacter pylori infection of gnotobiotic piglets

Clinical isolates of Helicobacter pylori, the gastric pathogen implicated in gastritis, peptic ulcers, and gastric cancer in humans, are diverse in traits likely to be important for colonization and disease. Here we report studies using a gnotobiotic piglet-H. pylori infection model to test for host-specific adaptation and to detect cocolonization by different strains. First, an H. pylori strain that initially had grown only weakly in piglets was adapted to them by spontaneous mutation and selection during 12 serial passages; this resulted in an increase in yield from about 10³ to > 10⁷ bacteria per g of mucosa. Second, piglets were fed mixtures of two different well-adapted strains and the presence of one or both strains was monitored by restriction analysis of a PCR-amplified flagellar (flaA) gene segment. The restriction fragment patterns from pools of bacteria indicated that both strains had colonized most piglets and that both strains were present at more than half of the individual biopsy sites, although often at unequal ratios. This suggests a microcolonial mode of growth with limited migration of bacteria between neighboring sites in the gastric mucosa. We propose that the gnotobiotic piglet-H. pylori infection model will be useful for testing how spontaneous mutation, selection, and DNA transfer between strains during mixed infection may each contribute to adaptation to specific hosts and the evolution of virulence of this important pathogen.