Haemophilus influenzae: imposter, mucosal pathobiont, and model organism

Haemophilus influenzae has served as a model organism in numerous ways over the last century. The relationship between H. influenzae and the influenza virus provided early insights into bacterial superinfections as a complication of viral infection. Studies of H. influenzae have shaped our understanding of virulence mechanisms used by many bacterial pathogens, such as polysaccharide capsules, natural competence for transformation, phase-variable gene expression, and type V protein secretion systems. H. influenzae has also been a trailblazer for the development of polysaccharide-protein conjugate vaccines and whole-genome sequencing technologies. In addition, H. influenzae has served as a key model organism for mucosal pathobionts, as it is famously associated with both asymptomatic colonization and a variety of disease states.