Within‐Host Evolution for the Invasiveness of Commensal Bacteria: an Experimental Study of Bacteremias Resulting fromHaemophilus influenzaeNasal Carriage

Abstract

Background. Many bacteria responsible for clinically relevant disease reside harmlessly in a large fraction of humans. Three explanations have been proposed to account for why these normally commensal bacteria occasionally cause invasive disease: host susceptibility, stochasticity in the host-bacteria interaction, and the evolution of invasive mutants in colonized hosts. Here we test the third of these hypotheses for the rare invasiveness of commensal bacteria: within-host evolution.