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

Abstract

The aim of this study was to investigate the presence of the three cdtABC genes responsible for production of cytolethal distending toxin (CDT) in Haemophilus ducreyi and Actinobacillus actinomycetemcomitans strains. Of 100 H. ducreyi strains from the culture collection of the University of Go Èteborg (CCUG), 27 strains with low or intermediate cytotoxic titre (<1 in 10 4 ) and 23 of the remaining isolates with a high cytotoxic titre (>1 in 10 4 ) were selected. Twenty-nine strains of H. ducreyi were isolated recently from patients with chancroid and 50 A. actinomycetemcomitans strains from patients with periodontitis. The cytotoxic activity on HEp-2 cells and the presence of cdtABC genes were studied by cytotoxicity assay of bacterial sonicates and PCR with primers speci®c for individual cdtA, B, and C genes of H. ducreyi in bacterial DNA preparations, respectively. All strains that manifested a cytotoxic titre in sonicate >1 in 100 possessed all the three cdt genes. Eighteen of the 50 strains selected from the culture collection were negative and 32 positive for cdt genes. As all strains with a high cytotoxic titre gave positive PCR results, it can be assumed that the remaining 50 strains, which have high cytotoxic titre, would have been positive as well. Thus, it can be estimated that 82% of the culture collection strains had cdtABC genes. Similarly, 24 (83%) of 29 recent H. ducreyi isolates expressed the CDT activity and displayed all cdtABC genes. Forty-three (86%) of 50 strains of the closely related A. actinomycetemcomitans, expressing a cytotoxic activity >1 in 100, also possessed all three genes. Furthermore, the nucleotide sequence of the cdtABC genes was highly conserved among H. ducreyi strains from different geographic areas. These results indicate that the majority of pathogenic H. ducreyi and A. actinomycetemcomitans strains express a CDT activity encoded by all three cdtABC.

Cytolethal distending toxin: a conserved bacterial genotoxin that blocks cell cycle progression, leading to apoptosis of a broad range of mammalian cell lineages

“…Strains of Campylobacter species Haem. ducreyi, A. actinomycetemcomitans, E. coli, Shigella species and EHS that lack a full complement of CDT genes and/or activity have been described elsewhere (Abuoun et al, 2005;Ahmed et al, 2001;Asakura et al, 2007b;Dassanayake et al, 2005b;Fabris et al, 2002;Hyma et al, 2005;Janka et al, 2003;Johnson & Lior, 1987;Solnick & Schauer, 2001;Yamano et al, 2003). …”

Differential effect of the cytolethal distending toxin of Actinobacillus actinomycetemcomitans on co-cultures of human oral cells

“…CDT is prevalent in A. actinomycetemcomitans strains. Ahmed et al (2001) found that 43 of 50 strains from periodontitis patients contained all three cdt genes and expressed CDT activity. In another study, PCR of subgingival plaque samples revealed that 13 of 106 diseased sites in 146 patients with aggressive and chronic periodontitis contained A. actinomycetemcomitans expressing all three cdt genes (Tan et al, 2002).…”

Perinuclear Localization of Internalized Outer Membrane Vesicles Carrying Active Cytolethal Distending Toxin from Aggregatibacter actinomycetemcomitans

“…actinomycetemcomitans is the only oral bacterial species known to produce CDT (70). A number of studies collectively support that CDT may be important in the pathogenesis of aggressive periodontitis (1,19,64), although the actual contribution of CDT to this disease is not yet understood. In vitro studies have revealed that CDT stimulated receptor activator of NF-B ligand (RANKL) in human gingival fibroblasts (HGF) (9), which comprise the major cell population of the gingival connective tissue (5).…”