Phenotype Evolution in Helicobacter pylori
Thursday, May 20, 1999 - 9:30am - 10:30am
Glenn Webb (Vanderbilt University)
Helicobacter pylori are bacteria that colonize the human stomach and are associated with diseases of the upper gastrointestinal tract. About half of the world's population is infected with H. pylori. Because colonization appears to confer benefits (reduced risk of esophageal diseases) as well as costs (increased risk of peptic ulcer disease and gastric adenocarcinoma), it is important to understand the biology of host-microbial interaction. Examination of the selective pressures on H. pylori provide a model for evolution of Lewis antigen phenotypes during the colonization of a human host. Mathematical models of Lewis antigen expression in H. pylori will be presented. The models will incorporate the following key elements: (1) H.pylori strains are highly diverse and continued variation is occuring during colonization; (2) H.pylori Lewis expression varies during colonization and host characteristics select for particular phenotypes; and (3) H.pylori strains have substantial ability to exchange DNA with other H.pylori strains thus providing opportunity for quasi-species development. The model consists of a nonlinear diffusion equation for the population density of bacteria with respect to Lewis antigen type. The equation incorporates the following elements of phenotype evolution: (1) mutation, (2) selection, and (3) recombination. Model simulations will be compared to data.