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Prevalence of cdtABC genes encoding cytolethal distending toxin among Haemophilus ducreyi and Actinobacillus

H J Ahmed, L A Svensson, L D Cope1

  • 1Department of Medical Microbiology and Immunology, University of Göteborg S-413 46 Göteborg, Sweden and *Department of Microbiology, Southwestern Medical Center, University of Texas, Dallas, USA.

Journal of Medical Microbiology
|October 16, 2001
PubMed

Insights

This study found that most Haemophilus ducreyi and Actinobacillus actinomycetemcomitans strains possess the cytolethal distending toxin (CDT) genes (cdtABC). The presence of these genes correlates with CDT activity, indicating their role in pathogenicity.

Area of Science:

  • Microbiology
  • Genetics
  • Bacterial Pathogenesis

Background:

  • Cytolethal distending toxin (CDT) is a key virulence factor produced by various Gram-negative bacteria.
  • Haemophilus ducreyi causes chancroid, and Actinobacillus actinomycetemcomitans is associated with periodontitis.
  • The cdtABC genes are essential for CDT production.

Purpose of the Study:

  • To investigate the presence and distribution of the cdtABC genes in H. ducreyi and A. actinomycetemcomitans.
  • To correlate the presence of cdtABC genes with cytolethal distending toxin (CDT) activity.

Main Methods:

  • Selection of H. ducreyi and A. actinomycetemcomitans strains from culture collections and recent clinical isolates.
  • Cytotoxicity assays on HEp-2 cells using bacterial sonicates.
  • Polymerase chain reaction (PCR) to detect the presence of cdtA, cdtB, and cdtC genes.

Main Results:

  • All tested strains exhibiting a cytotoxic titre of ≥ 1 in 100 possessed all three cdtABC genes.
  • Approximately 82% of culture collection H. ducreyi strains and 83% of recent H. ducreyi isolates carried the cdtABC genes.
  • 86% of A. actinomycetemcomitans strains with cytotoxic activity also possessed the cdtABC genes, with conserved nucleotide sequences.

Conclusions:

  • The majority of pathogenic H. ducreyi and A. actinomycetemcomitans strains harbor the cdtABC genes.
  • The presence of cdtABC genes is strongly associated with cytolethal distending toxin (CDT) activity in these bacteria.
  • These findings highlight the conserved role of cdtABC in the pathogenicity of H. ducreyi and A. actinomycetemcomitans.

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