Affiliation:
1. Department of Food Science, Cornell University, Ithaca, New York, USA
2. Department of Population Medicine and Diagnostic Sciences, Cornell University, Ithaca, New York, USA
3. Department of Biomedical Sciences, Cornell University, Ithaca, New York, USA
Abstract
ABSTRACT
The
Salmonella
cytolethal distending toxin (S-CDT), first described as the “typhoid toxin” in
Salmonella enterica
subsp.
enterica
serotype Typhi, induces DNA damage in eukaryotic cells. Recent studies have shown that more than 40 nontyphoidal
Salmonella
(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 (
pltB
) and a bacteriophage muramidase predicted to play a role in toxin export (
ttsA
) does not abolish toxin activity in the S-CDT-positive NTS
Salmonella enterica
subsp.
enterica
serotype Javiana. However,
S.
Javiana strains harboring deletions of both
pltB
and its homolog
artB
, had a complete loss of S-CDT activity, suggesting that
S.
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
2
/M phases of the cell cycle and did not result in apoptosis or cell death. Compared to mice infected with a Δ
cdtB
strain, mice infected with wild-type
S.
Javiana had significantly higher levels of
S.
Javiana in the liver, but not in the spleen, ileum, or cecum. Overall, we show that production of active S-CDT by NTS serotype
S.
Javiana requires different genes (
cdtB
,
pltA
, and either
pltB
or
artB
) for expression of biologically active toxin than those reported for S-CDT production by
S.
Typhi (
cdtB
,
pltA
,
pltB
, and
ttsA
). However, as in
S.
Typhi, NTS S-CDT influences the outcome of infection both
in vitro
and
in vivo
.
IMPORTANCE
Nontyphoidal
Salmonella
(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
in vitro
and
in vivo
, highlighting S-CDT as an important virulence factor for nontyphoidal
Salmonella
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
S.
Javiana has different genetic requirements than
S.
Typhi, for the production and export of active S-CDT.
Funder
U.S. Department of Agriculture
Publisher
American Society for Microbiology