Current vaccines against Haemophilus influenzae type b have reduced the incidence of H. influenzae type b invasive diseases. However, they provide no protection against nontypable strains which remain a common cause of otitis media, the most common infection of childhood, and pneumonia. H. influenzae has an absolute growth requirement for heme and the human body is its sole niche. We have characterized several of the heme and iron acquisition systems of H. influenzae and shown that their expression is regulated by iron/heme levels in the growth media. In addition we have shown that the genes are expressed in vivo in both humans and animal models, indicating that the in vivo environment is similarly heme restricted. However our understanding of the systems involved in the acquisition of this essential nutrient and their regulation remains incomplete. We propose a genomics analysis to define the genes whose expression is regulated by iron and heme levels (the FeHm regulon) and to determine their role in virulence in animal models of disease. The FeHm regulon has been defined in one sequenced H. influenzae strain using microarray technology, and we will use the same approach to define the FeHm regulon in two additional sequenced strains. Following identification of the genes we will construct pools of signature-tagged mutants for analysis in vivo in three animal models (the chinchilla model of otitis media and nasopharyngeal colonization, the rat model of invasive disease and the rat model of persistence in the lung). Mutants will additionally be compared to wildtype strains for in vitro growth with various heme sources, as well as protection against heme toxicity and oxidative damage and for their ability to form biofilms. These studies will provide a framework for advancing our understanding of the iron/heme acquisition systems of H. influenzae with further potential for providing preventive and treatment strategies for H. influenzae disease.

Public Health Relevance

Haemophilus influenzae is a major cause of childhood ear infections and pneumonia in adults who have other conditions, such as cystic fibrosis or HIV/AIDS, predisposing them to infections. We are seeking to understand what makes Haemophilus influenzae able to cause these infections and especially how it gets important nutrients, such as iron, when it is causing an infection. Understanding these mechanisms has the potential to lead to novel treatments for and/or vaccines to prevent Haemophilus influenzae infections.

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
Research Project (R01)
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Bacterial Pathogenesis Study Section (BACP)
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Khambaty, Farukh M
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University of Oklahoma Health Sciences Center
Schools of Medicine
Oklahoma City
United States
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Hempel, Randy J; Morton, Daniel J; Seale, Thomas W et al. (2013) The role of the RNA chaperone Hfq in Haemophilus influenzae pathogenesis. BMC Microbiol 13:134
Whitby, Paul W; VanWagoner, Timothy M; Seale, Thomas W et al. (2013) Comparison of transcription of the Haemophilus influenzae iron/heme modulon genes in vitro and in vivo in the chinchilla middle ear. BMC Genomics 14:925
Morton, Daniel J; Hempel, Randy J; Whitby, Paul W et al. (2012) An invasive Haemophilus haemolyticus isolate. J Clin Microbiol 50:1502-3
Whitby, Paul W; Morton, Daniel J; Vanwagoner, Timothy M et al. (2012) Haemophilus influenzae OxyR: characterization of its regulation, regulon and role in fitness. PLoS One 7:e50588
Morton, Daniel J; Hempel, Randy J; Seale, Thomas W et al. (2012) A functional tonB gene is required for both virulence and competitive fitness in a chinchilla model of Haemophilus influenzae otitis media. BMC Res Notes 5:327
Whitby, Paul W; VanWagoner, Timothy M; Morton, Daniel J et al. (2012) Signature-tagging of a bacterial isolate demonstrates phenotypic variability of the progeny in vivo in the absence of defined mutations. J Microbiol Methods 91:336-40
Whitby, Paul W; Seale, Thomas W; Morton, Daniel J et al. (2010) Characterization of the Haemophilus influenzae tehB gene and its role in virulence. Microbiology 156:1188-200
Morton, Daniel J; Turman, Elizabeth J; Hensley, Patrick D et al. (2010) Identification of a siderophore utilization locus in nontypeable Haemophilus influenzae. BMC Microbiol 10:113
Morton, Daniel J; Seale, Thomas W; Vanwagoner, Timothy M et al. (2009) The dppBCDF gene cluster of Haemophilus influenzae: Role in heme utilization. BMC Res Notes 2:166
Whitby, Paul W; Seale, Thomas W; VanWagoner, Timothy M et al. (2009) The iron/heme regulated genes of Haemophilus influenzae: comparative transcriptional profiling as a tool to define the species core modulon. BMC Genomics 10:6

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