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Background  For many putative  Salmonella enterica  subsp.  enterica  virulence genes, functional characterization across serovars has been limited. Cytolethal distending toxin B (CdtB) is an incompletely characterized virulence factor that is found not only in  Salmonella enterica  subsp.  enterica  serovar Typhi ( Salmonella  Typhi) and dozens of Gram negative bacterial pathogens, but also in non-typhoidal  Salmonella  (NTS) serovars.    Methods  A comparative genomics approach was performed to characterize sequence conservation of the typhoid toxin (TT), encoded in the CdtB-islet, between  Salmonella  Typhi and NTS serovars. The cytotoxic activity of representative  Salmonella enterica  subsp.  enterica  serovars Javiana, Montevideo and Schwarzengrund strains and their respective isogenic  cdtB  mutants was determined in human intestinal epithelial Henle-407 cells by assessment of cell cycle progression of infected cells using fluorescence-activated cell sorting (FACS). Two-way analysis of variance (ANOVA) was used to determine whether  cdtB  deletion had a significant (p < 0.05) effect on the percentage of Henle-407 cells at each stage of the cell cycle.    Results  Here we show that a CdtB-islet encoding the cytolethal distending toxin B (CdtB), pertussis-like toxin A (PltA), and pertussis-like toxin B (PltB) is present in a dozen NTS serovars and that these proteins have a high level of sequence conservation and each form monophyletic clades with corresponding  Salmonella  Typhi genes. Human epithelial Henle-407 cells infected with three representative CdtB-encoding NTS serovars displayed G 2 /M phase cell cycle arrest that was absent in cells infected with corresponding isogenic  cdtB  null mutants (p < 0.0001 for the factor ∆ cdtB  deletion).    Conclusion  Our results show that CdtB encoded by NTS serovars has a genomic organization, amino acid sequence conservation and biological activity similar to the TT, and thus, may contribute to disease pathogenesis.    Electronic supplementary material  The online version of this article (doi:10.1186/s13099-015-0065-1) contains supplementary material, which is available to authorized users.

Characterization of the cytolethal distending toxin (typhoid toxin) in non-typhoidal Salmonella serovars