Continuous Microevolution Accelerates Disease Progression during Sequential Episodes of Infection.

Bacteria adapt to dynamic changes in the host during chronic and recurrent infections. Bacterial microevolution is one type of adaptation that imparts a selective advantage. We hypothesize that recurrent episodes of disease promote microevolution through genetic mutations that modulate disease severity. We use a pre-clinical model of otitis media (OM) to determine the potential role for microevolution of nontypeable Haemophilus influenzae (NTHI) during sequential episodes of disease. Whole genome sequencing reveals microevolution of hemoglobin binding and lipooligosaccharide (LOS) biosynthesis genes, suggesting that adaptation of these systems is critical for infection. These OM-adapted strains promote increased biofilm formation, inflammation, stromal fibrosis, and an increased propensity to form intracellular bacterial communities (IBCs). Remarkably, IBCs remain for at least one month following clinical resolution of infection, suggesting an intracellular reservoir as a nidus for recurrent OM. Additional approaches for therapeutic design tailored to combat this burdensome disease will arise from these studies.