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Applied and Environmental Microbiology, October 2005, p. 5685-5691, Vol. 71, No. 10
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.10.5685-5691.2005

Salmonella enterica Virulence Genes Are Required for Bacterial Attachment to Plant Tissue

Jeri D. Barak,1* Lisa Gorski,1 Pejman Naraghi-Arani,1,{dagger} and Amy O. Charkowski2

Produce Safety and Microbiology Research Unit, WRRC/ARS/USDA, 800 Buchanan St., Albany, California 94710,1 Department of Plant Pathology, Russell Laboratories, 1630 Linden Dr., University of Wisconsin-Madison, Madison, Wisconsin 537062

Received 19 August 2004/ Accepted 28 April 2005

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.

* Corresponding author. Mailing address: USDA, ARS, WRRC, Produce Safety and Microbiology, 800 Buchanan St., Albany, CA 94710. Phone: (510) 559-6180. Fax: (510) 559-6162. E-mail: jbarak{at}pw.usda.gov.

{dagger} Present address: Biodefense Division, Lawrence Livermore National Lab, 7000 East St., Livermore, CA 94550.

Applied and Environmental Microbiology, October 2005, p. 5685-5691, Vol. 71, No. 10
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.10.5685-5691.2005




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