The Typhoid Toxin Produced by the Nontyphoidal Serotype Javiana Is Required for Induction of a DNA Damage Response and Systemic Spread .

The cytolethal distending toxin (S-CDT), first described as the "typhoid toxin" in subsp. serotype Typhi, induces DNA damage in eukaryotic cells. Recent studies have shown that more than 40 nontyphoidal (NTS) serotypes carry genes that encode S-CDT, yet very little is known about the activity, function, and role of S-CDT in NTS. Here we show that deletion of genes encoding the binding subunit () and a bacteriophage muramidase predicted to play a role in toxin export () does not abolish toxin activity in the S-CDT-positive NTS subsp. serotype Javiana. However, Javiana strains harboring deletions of both and its homolog , had a complete loss of S-CDT activity, suggesting that Javiana carries genes encoding two variants of the binding subunit. S-CDT-mediated DNA damage, as determined by phosphorylation of histone 2AX (H2AX), producing phosphorylated H2AX (γH2AX), was restricted to epithelial cells in S and G/M phases of the cell cycle and did not result in apoptosis or cell death. Compared to mice infected with a Δ strain, mice infected with wild-type Javiana had significantly higher levels of Javiana in the liver, but not in the spleen, ileum, or cecum. Overall, we show that production of active S-CDT by NTS serotype Javiana requires different genes (, , and either or ) for expression of biologically active toxin than those reported for S-CDT production by Typhi (, , , and ). However, as in Typhi, NTS S-CDT influences the outcome of infection both and Nontyphoidal (NTS) are a major cause of bacterial food-borne illness worldwide; however, our understanding of virulence mechanisms that determine the outcome and severity of nontyphoidal salmonellosis is incompletely understood. Here we show that S-CDT produced by NTS plays a significant role in the outcome of infection both and , highlighting S-CDT as an important virulence factor for nontyphoidal serotypes. Our data also contribute novel information about the function of S-CDT, as S-CDT-mediated DNA damage occurs only during certain phases of the cell cycle, and the resulting damage does not induce cell death as assessed using a propidium iodide exclusion assay. Importantly, our data support that, despite having genetically similar S-CDT operons, NTS serotype Javiana has different genetic requirements than Typhi, for the production and export of active S-CDT.