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Salmonella enterica Virulence Genes Are Required for Bacterial Attachment to
Plant Tissue.
Appl Environ Microbiol. 2005 Oct;71(10):5685-91.
Barak JD, Gorski L, Naraghi-Arani P, Charkowski AO.
USDA, ARS, WRRC, Produce Safety and Microbiology,
800
Buchanan St., Albany, CA 94710. jbarak@pw.usda.gov.
Numerous Salmonella enterica food-borne illness outbreaks have been associated
with contaminated vegetables, in particular sprouted seeds, and the incidence of
reported contamination has steadily risen. In order to understand the physiology
of S. enterica serovar Newport on plants, a screen was developed to identify
transposon mutants that were defective in attachment to alfalfa sprouts. Twenty
independent mutants from a pool of 6,000 were selected for reduced adherence to
alfalfa sprouts. Sixty-five percentage of these mutants had insertions in
uncharacterized genes. Among the characterized genes were strains with
insertions in the intergenic region between agfB, the surface-exposed
aggregative fimbria (curli) nucleator, and agfD, a transcriptional regulator of
the LuxR superfamily, and rpoS, the stationary-phase sigma factor. Both AgfD and
RpoS have been reported to regulate curli and cellulose production and RpoS
regulates other adhesins such as pili. The intergenic and rpoS mutants were
reduced in initial attachment to alfalfa sprouts by 1 log unit compared to the
wild type. Mutations of agfA, curli subunit, and agfB in S. enterica serovar
Enteritidis differentially affected attachment to plant tissue. The agfA
mutation was not reduced in ability to attach to or colonize alfalfa sprouts,
whereas the agfB mutation was reduced. Thus, agfB alone can play a role in
attachment of S. enterica to plant tissue. These results reveal that S. enterica
genes important for virulence in animal systems are also required for
colonization of plants, a secondary host that can serve as a vector of S.
enterica from animal to animal.
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