Abstract
Abstract
Background
Salmonella enterica
serovar Typhimurium is a major foodborne pathogen worldwide.
S.
Typhimurium encodes type III secretion systems via
Salmonella
pathogenicity islands (SPI), producing the major effector proteins of virulence. Previously, we identified two genes of
Salmonella
pyruvate metabolism that were up-regulated during chicken cell infection: pyruvate formate lyase I (
pflB
) and bifunctional acetaldehyde-CoA/alcohol dehydrogenase (
adhE
). We were therefore interested in examining the role these genes may play in the transmission of
Salmonella
to humans.
Methods
Mutant strains of
Salmonella
with single gene deletions for
pflB
and
adhE
were created. Invasion and growth in human HCT-8 intestinal epithelial cells and THP-1 macrophages was examined. Quantitative PCR was performed on 19 SPI-1 genes.
Results
In HCT-8 cells, both mutant strains had significantly higher intracellular counts than the wild-type from 4 to 48 h post-infection. Various SPI-1 genes in the mutants were up-regulated over the wild-type as early as 1 h and lasting until 24 h post-infection. In THP-1 cells, no significant difference in internal
Salmonella
counts was observed; however, SPI-1 genes were largely down-regulated in the mutants during the time-course of infection. We also found five SPI-1 genes -
hilA
,
hilC hilD
,
sicP
and
rtsA
- which were up-regulated in at least one of the mutant strains in log-phase broth cultures alone. We have therefore identified a set of SPI-1 virulence genes whose regulation is effected by the central metabolism of
Salmonella
.