Purpose: The goals of this study were to (i) determine the distribution of CDT among NTS serotypes, and (ii) characterize differences in the outcome of infection with CDT positive and CDT negative strains using a cell culture model system.
Methods: A total of 866 strains belonging to 21 of the most frequently isolated NTS serotypes from cases of human salmonellosis were screened using PCR amplification of internal regions of cdtB, pltA, and pltB, encoding the CDT. Toxin activity was confirmed using flow cytometry to compare cell cycle progression of HeLa CCL-2 cells infected with CDT-positive and CDT-negative strains.
Results: Genes encoding a complete CDT were detected in 100% of strains (n=50 tested per serotype) for serotypes Javiana, Montevideo, and Oranienburg, and for 50% (4 out of 8) of strains for serotype Mississippi. HeLa cells infected with wild type strains of Javiana, Montevideo, and Mississippi exhibited a characteristic G2/M phase arrest, indicative of these strains producing an active CDT. By comparison, HeLa cells infected with either mutants lacking the gene encoding the active component of CDT, or CDT-negative strains, did not arrest in the G2/M phase.
Significance: These results suggest that infection with CDT-positive strains of NTS impart DNA damage and may result in a different illness compared to CDT-negative strains. Furthermore, these results are relevant for determining the public health impact of CDT-positive NTS infections.