Effect of lipooligosaccharide mutations of Haemophilus influenzae on the middle and inner ears

Objective: The purpose of this study was to determine the virulence of nontypeable Haemophilus influenzae 2019 (NTHi 2019) and its two lipooligosaccharide (LOS) mutant strains, B29 (gene htrB) and DK1 (gene rfaD), and compare their effect on the middle ear, round window membrane, and inner ear. Results: Fifteen chinchillas were divided into three equal groups and their bullas inoculated bilaterally with 0.5 ml of 10² CFU/ml of parent NTHi 2019, B29 or DK1 mutant strains. Two days after inoculation all animals had otitis media and inflamed middle ear mucosa. There was a trend of greater thickness and infiltration of the round window membrane in animals inoculated with the wild-type NTHi strain compared to the mutant strains and a significant increase in both inflammatory cell infiltration and bacteria presence in the scala tympani area of the inner ear. Strial edema was only observed in the wild-type-inoculated group. Conclusions: LOS mutants of NTHi appear to have a reduced ability to pass through the round window membrane resulting in less inner ear inflammation and pathological changes.