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J Infect Dis. 2015 Aug 15;212(4):645-53. doi: 10.1093/infdis/jiv103. Epub 2015 Feb 23.

Selection and Counterselection of Hia Expression Reveals a Key Role for Phase-Variable Expression of Hia in Infection Caused by Nontypeable Haemophilus influenzae.

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Institute for Glycomics, Griffith University, Gold Coast, Australia.
Department of Pediatrics, Saint Louis University School of Medicine Pediatric Research Institute, Cardinal Glennon Children's Medical Center, Saint Louis, Missouri.
Center for Microbial Pathogenesis, The Research Institute at Nationwide Children's Hospital and The Ohio State University College of Medicine, Columbus.


Hia is a major adhesin of nontypeable Haemophilus influenzae (NTHi) and has long been investigated as a vaccine candidate. Here we show that Hia phase variation is controlled by changes in the length of a polythymidine tract located in the hia promoter. Studies of an invasive clinical isolate (strain R2866) show that strains expressing high Hia levels are more efficiently killed by opsonophagocytosis. An opsonophagocytic assay was used to select for a subpopulation of variants that expressed a low level of Hia, which facilitated their escape from killing by anti-Hia antisera. Conversely, a subpopulation of variants expressing a high level of Hia was selected for during passaging through Chang cells. In both cases, phase variation of Hia expression corresponded directly with discrete modal changes in polythymidine tract length. In the chinchilla model of NTHi infection, we observed consistent selection for high Hia expression upon nasopharyngeal colonization, confirming the key role of phase-variable expression of Hia within a specific niche in vivo.


Haemophilus; adhesion; colonization; phase variation

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