Evaluation of phase variation of nontypeable Haemophilus influenzae lipooligosaccharide during nasopharyngeal colonization and development of otitis media in the chinchilla model

Nontypeable Haemophilus influenzae (NTHI) has four loci, lic-1 to lic-3 and lgtC, that generate phase-variable lipooligosaccharide (LOS) structures. lic-1, which is required for the expression of phosphorylcholine (ChoP), is the best characterized and is associated with an enhanced ability of H. influenzae to persist within the nasopharynges of infant rats. Recent data indicate that LOS impacts various aspects of NTHI virulence in the chinchilla model of nasopharyngeal colonization and otitis media (OM). In this study the effects of Chop expression and the sequences of lic-1 to lic-3 and lgtC of NTHI strain 2019 were evaluated in the chinchilla OM model. Nasopharyngeal colonization data showed that a switch from the ChoP(-) to the ChoP(+) phenotype was observed as early as day 3 after intranasal inoculation. Chinchillas colonized by strains with the ChoP(+) phenotype demonstrated a significantly higher level of NTHI 2019 per milliliter of nasal lavage fluid than chinchillas colonized with predominantly the ChoP(-) variant (P < 0.05). The concentration of cells with the ChoP(+) phenotype in the middle ear was 3 log units higher than that of cells with the ChoP(-) variant (P < 0.01). There was a statistically significant association between ChoP(+) expression in the nasal lavage and the development of OM with culture-positive middle ear fluids in this model. These data suggest that expression of the ChoP(+) phenotype promotes enhanced nasolpharyngeal colonization and development of OM.