Evidence for capsule gene sequences among pharyngeal isolates of nontypeable Haemophilus influenzae.


Journal Article

Haemophilus influenzae is a common commensal organism of the human respiratory tract and is an important cause of localized and systemic disease. While isolates recovered from the respiratory tract are generally nonencapsulated (serologically nontypeable), isolates from systemic sites typically express a polysaccharide capsule. To explore the possibility that nontypeable strains evolved from encapsulated organisms, a series of serologically nontypeable isolates were examined for the presence of capsule gene sequences. Pharyngeal isolates (123) were collected from healthy 3-year-old Finnish children and examined by Southern hybridization with pUO38, a plasmid that contains one complete set of cap genes from an H. influenzae type b strain. Twenty-four isolates (20%) demonstrated homology with capsule-specific sequences. Of these 24, 18 in addition to 14 others had evidence of one or more copies of IS1016, an insertion element that has been associated with encapsulation in H. influenzae. These results support the hypothesis that nontypeable strains of H. influenzae arose from an encapsulated ancestor. Possibly the selective pressure driving the loss of encapsulation relates to the disadvantage associated with encapsulation during respiratory tract colonization.

Full Text

Cited Authors

  • St Geme, JW; Takala, A; Esko, E; Falkow, S

Published Date

  • February 1994

Published In

Volume / Issue

  • 169 / 2

Start / End Page

  • 337 - 342

PubMed ID

  • 8106767

Pubmed Central ID

  • 8106767

Electronic International Standard Serial Number (EISSN)

  • 1537-6613

International Standard Serial Number (ISSN)

  • 0022-1899

Digital Object Identifier (DOI)

  • 10.1093/infdis/169.2.337


  • eng