Haemophilus ducreyi requires the flp gene cluster for microcolony formation in vitro.
Haemophilus ducreyi, the etiologic agent of chancroid, has been shown to form microcolonies when cultured in the presence of human foreskin fibroblasts. We identified a 15-gene cluster in H. ducreyi that encoded predicted protein products with significant homology to those encoded by the tad (for tight adhesion) locus in Actinobacillus actinomycetemcomitans that is involved in the production of fimbriae by this periodontal pathogen. The first three open reading frames in this H. ducreyi gene cluster encoded predicted proteins with a high degree of identity to the Flp (fimbria-like protein) encoded by the first open reading frame of the tad locus; this 15-gene cluster in H. ducreyi was designated flp. RT-PCR analysis indicated that the H. ducreyi flp gene cluster was likely to be a polycistronic operon. Mutations within the flp gene cluster resulted in an inability to form microcolonies in the presence of human foreskin fibroblasts. In addition, the same mutants were defective in the ability to attach to both plastic and human foreskin fibroblasts in vitro. An H. ducreyi mutant with an inactivated tadA gene exhibited a small decrease in virulence in the temperature-dependent rabbit model for experimental chancroid, whereas another H. ducreyi mutant with inactivated flp-1 and flp-2 genes was as virulent as the wild-type parent strain. These results indicate that the flp gene cluster is essential for microcolony formation by H. ducreyi, whereas this phenotypic trait is not linked to the virulence potential of the pathogen, at least in this animal model of infection.
Nika
Joseph R
JR
Department of Microbiology, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA.
Latimer
Jo L
JL
Ward
Christine K
CK
Blick
Robert J
RJ
Wagner
Nikki J
NJ
Cope
Leslie D
LD
Mahairas
Gregory G
GG
Munson
Robert S
RS
Hansen
Eric J
EJ
D000595:Amino Acid Sequence; D001422:Bacterial Adhesion / Q000502:physiology; D001426:Bacterial Proteins / Q000235:genetics*; D001483:Base Sequence; D002460:Cell Line; D004269:DNA, Bacterial; D005347:Fibroblasts / Q000166:cytology / Q000382:microbiology; D005796:Genes; D005798:Genes, Bacterial / Q000502:physiology*; D005816:Genetic Complementation Test; D006191:Haemophilus ducreyi / Q000235:genetics / Q000254:growth & development* / Q000472:pathogenicity / Q000502:physiology; D006801:Humans; D008969:Molecular Sequence Data; D005810:Multigene Family / Q000502:physiology*; D016296:Mutagenesis; D016366:Open Reading Frames; D009876:Operon; D010969:Plastics; D017386:Sequence Homology, Amino Acid; D014158:Transcription, Genetic; D014774:Virulence
D001426:Bacterial Proteins; D004269:DNA, Bacterial; D010969:Plastics