Genes involved in Haemophilus influenzae type b capsule expression are frequently amplified

J Infect Dis. 1993 Feb;167(2):356-64. doi: 10.1093/infdis/167.2.356.


The genes involved in Haemophilus influenzae type b capsule expression are present as a duplication of an approximately 18-kb DNA segment (the Cap b locus). It has been shown previously that recombination occurs between the two copies of the repeat, resulting in deletion of one copy and loss of capsule expression at frequencies of 0.1%-0.5%. The present study tested the hypothesis that the duplicated arrangement could serve as a template for further amplification of capsule gene sequences. Southern hybridization analysis of 66 type b invasive isolates showed that amplifications exist and are moderately common (23/66 were amplified). In addition to three copies of the 18-kb repeat, four copies were detected in some strains, and up to five copies in 1 isolate. By ELISA, a five-copy strain made about six times more capsular polysaccharide than did an isogenic two-copy derivative. The evolutionary significance of the duplicated arrangement may be its ability to rapidly amplify under conditions where it is advantageous to produce more capsule.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Bacterial Capsules / genetics*
  • Bacterial Vaccines / analysis
  • Bacterial Vaccines / biosynthesis
  • Blotting, Southern
  • DNA, Bacterial / analysis
  • District of Columbia
  • Enzyme-Linked Immunosorbent Assay
  • Finland
  • Gene Amplification*
  • Gene Expression Regulation, Bacterial*
  • Haemophilus Infections / microbiology*
  • Haemophilus Vaccines*
  • Haemophilus influenzae / genetics*
  • Haemophilus influenzae / pathogenicity
  • Humans
  • Nucleic Acid Hybridization
  • Polysaccharides, Bacterial / analysis
  • Polysaccharides, Bacterial / biosynthesis
  • Restriction Mapping
  • Virulence


  • Bacterial Vaccines
  • DNA, Bacterial
  • Haemophilus Vaccines
  • Haemophilus influenzae type b polysaccharide vaccine
  • Polysaccharides, Bacterial