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United States Department of Agriculture

Agricultural Research Service

Title: Salmonella Enterica Virulence Genes Are Required for Bacterial Attachment to Plant Tissue

Authors
item Barak Cunningham, Jeri
item Gorski, Lisa
item Naraghi-Arani, Pejman - LAWRENCE LIVERMORE NAT. L
item Charkowski, Amy - UNIV. OF WISCONSON, MADI

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 28, 2005
Publication Date: October 1, 2005
Citation: Barak Cunningham, J.D., Gorski, L.A., Naraghi-Arani, P., Charkowski, A. 2005. Salmonella enterica virulence genes are required for bacterial attachment to plant tissue. AEM.71.10.5685-5691

Interpretive Summary: Numerous Salmonella enterica foodborne 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 Salmonella on plants, a screen was developed to identify transposon mutants that were defective in attachment to alfalfa sprouts. Twenty mutants from a pool of 6,000 were selected for reduced adherence to alfalfa sprouts. Sixty-five percent of these mutants had insertions in uncharacterized genes. Among the previously characterized genes were strains with insertions in the intergenic region between agfB, the surface-exposed aggregative fimbriae (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 mutant strains were reduced in initial attachment to alfalfa sprouts by one log unit when compared to the wild type. Mutations of agfA, curli subunit, and agfB in S. enterica Enteritidis differentially affected attachment to plant tissue. The agfA mutation was not reduced in ability to attach to or colonize alfalfa sprouts while the agfB mutation was reduced. Thus agfB alone can play a role in attachment of Salmonella to plant tissue. These results reveal that Salmonella genes important for virulence in animal systems are also required for colonization of plants, a secondary host that can serve as a vector of Salmonella from animal to animal.

Technical Abstract: Numerous Salmonella enterica foodborne 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 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 percent 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 fimbriae (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 one log unit when compared to the wild type. Mutations of agfA, curli subunit, and agfB in S. enterica Enteritidis differentially affected attachment to plant tissue. The agfA mutation was not reduced in ability to attach to or colonize alfalfa sprouts while 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.

Last Modified: 7/28/2014
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