Dysregulation of tryptophan biosynthesis as a putative treatment approach for nontypeable Haemophilus influenzae, a causative agent of otitis media

Abstract

Bacterial adaptation to the nutritional environment of the host is critical for infection. We hypothesize that microevolution due to nutrient stress enhances invasion, intracellular bacterial community formation (IBC), and persistence of nontypeable Haemophilus influenzae (NTHI). We previously identified an NTHI mutant that arose during prolonged nutrient deprivation that promoted in vitro persistence and during experimental otitis media (OM). We determined that a single mutation in the gene encoding cyclic AMP phosphodiesterase reprioritizes NTHI metabolism during biofilm growth in this evolved strain. There was a significant increase in all proteins involved in tryptophan metabolism. Given the importance of tryptophan and tryptophan metabolites in host immunity and bacterial virulence, the contribution of tryptophan biosynthesis on NTHI pathogenesis and intracellular survival was evaluated. We generated a panel of mutant strains impaired in tryptophan biosynthesis, import, or both. Loss of tryptophan synthesis significantly inhibited bacterial growth. We also showed that dysregulation of tryptophan biosynthesis leads to accumulation of the tryptophan metabolite indole which we hypothesize results in indole toxicity of NTHI. We subsequently found that tryptophan biosynthesis pathway impairment significantly inhibited NTHI IBC formation in both human bronchial epithelial cells and in a pre-clinical chinchilla model of OM. When competed against the parent strain, loss of either tryptophan synthesis or import resulted in increased fitness in a chinchilla model. Taken together, NTHI adaptation to nutrient sequestration dysregulates tryptophan biosynthesis and is associated with reduced bacterial viability, possibly through the accumulation of indole. Further, this dysregulation of tryptophan biosynthesis reduces formation of IBCs, which will impact persistence of NTHI. The implications of these discoveries will therefore help guide the future developments of therapeutics for treatment of OM.R21-AI164077 from NIH/NIAID (KMM)A one-year embargo was granted for this item.Academic Major: Biomedical Scienc