Analysis of Nontypeable Haemophilus influenzae Phase-Variable Genes During Experimental Human Nasopharyngeal Colonization

Background. Studies of nontypeable Haemophilus influenzae (NTHi) have demonstrated that a number of genes associated with infectivity have long repeat regions associated with phase variation in expression of the respective gene. The purpose of this study was to determine the genes that underwent phase variation during a 6-day period of experimental human nasopharyngeal colonization. Methods. Strain NTHi 2019StrR1 was used to colonize the nasopharynx of human subjects in a study of experimental colonization. Thirteen phase-variable genes were analyzed in NTHi 2019StrR1. Samples of NTHi 2019StrR1 were cultured from subjects during the 6-day colonization period. We used capillary electrophoresis and Roche 454 pyrosequencing to determine the number of repeats in each gene from each sample. Results. A significant number of samples switched licA and igaB from phase off in the inoculated strain to phase on during the 4-day period of observation. lex2A also showed variability as compared to baseline, but the differences were not significant. The remaining genes showed no evidence of phase variation. Conclusions. Our studies suggest that the phase-on genotypes of licA and igaB are important for early human nasopharynx colonization. lex2A showed a trend from phase off to phase on, suggesting a potentially important role in the colonization process.