Expression and analysis of a cytolethal distending toxin (cdt) gene operon in Campylobacter lari

Dynamic Duo-The Salmonella Cytolethal Distending Toxin Combines ADP-Ribosyltransferase and Nuclease Activities in a Novel Form of the Cytolethal Distending Toxin

The cytolethal distending toxin (CDT) is a well characterized bacterial genotoxin encoded by several Gram-negative bacteria, including Salmonella enterica (S. enterica). The CDT produced by Salmonella (S-CDT) differs from the CDT produced by other bacteria, as it utilizes subunits with homology to the pertussis and subtilase toxins, in place of the traditional CdtA and CdtC subunits. Previously, S-CDT was thought to be a unique virulence factor of S. enterica subspecies enterica serotype Typhi, lending to its classification as the “typhoid toxin.” Recently, this important virulence factor has been identified and characterized in multiple nontyphoidal Salmonella (NTS) serotypes as well. The significance of S-CDT in salmonellosis with regards to the: (i) distribution of S-CDT encoding genes among NTS serotypes, (ii) contributions to pathogenicity, (iii) regulation of S-CDT expression, and (iv) the public health implication of S-CDT as it relates to disease severity, are reviewed here.

Campylobacter hyointestinalis Isolated from Pigs Produces Multiple Variants of Biologically Active Cytolethal Distending Toxin

Campylobacter hyointestinalis isolated from swine with proliferative enteritis often is considered to be pathogenic. While the precise virulence mechanisms of this species remain unclear, we have recently identified a cytolethal distending toxin (cdt) gene cluster in C. hyointestinalis isolated from a patient with diarrhea (W. Samosornsuk et al., J Med Microbiol, 27 July 2015, http://dx.doi.org/10.1099/jmm.0.000145). However, the sequences of the cdt genes in C. hyointestinalis were found to be significantly different and the gene products are immunologically distinct from those of other Campylobacter species. In this study, we demonstrate the presence of a second variant of the cdt gene cluster in C. hyointestinalis, designated cdt-II, while the former is named cdt-I. Sequencing of the cdt-II gene cluster and deduced amino acid sequences revealed that homologies between the subunits CdtA, CdtB, and CdtC of ChCDT-I and ChCDT-II are 25.0, 56.0, and 24.8%, respectively. Furthermore, the CdtB subunit of ChCDT-II was found to be immunologically unrelated to that of ChCDT-I by Ouchterlony double gel diffusion test. Recombinant ChCDT-II also induced cell distention and death of HeLa cells by blocking the cell cycle at G2/M phase. Interestingly, the cdt-II genes were detected in all 23 animal isolates and in 1 human isolate of C. hyointestinalis, and 21 of these strains carried both cdt-I and cdt-II gene clusters. Altogether, our results indicate that ChCDT-II is an important virulence factor of C. hyointestinalis in animals.