Jeri D. Barak,1
Courtney E. Jahn,2
Deanna L. Gibson,3,4 and
Amy O. Charkowski2
1Produce Safety and Microbiology Research Unit, United States Department of Agriculture--Agricultural Research Service, Albany, CA 94710, U.S.A.; 2Department of Plant Pathology, Rm 682 Russell Laboratories, 1630 Linden Dr., University of Wisconsin-Madison, Madison, WI 53706, U.S.A.; 3Department of Biochemistry and Microbiology, University of Victoria, Victoria V8W 3P6, British Columbia, Canada; 4Department of Pediatrics, University of British Columbia, Vancouver V5Z 4H4, British Columbia, Canada
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Accepted 17 April 2007.
Numerous salmonellosis outbreaks have been associated with vegetables, in particular sprouted seed. Thin aggregative fimbriae (Tafi), a component of the extracellular matrix responsible for multicellular behavior, are important for Salmonella enterica attachment and colonization of plants. Here, we demonstrate that the other surface polymers composing the extracellular matrix, cellulose, and O-antigen capsule also play a role in colonization of plants. Mutations in bacterial cellulose synthesis (bcsA) and O-antigen capsule assembly and translocation (yihO) reduced the ability to attach to and colonize alfalfa sprouts. A colanic acid mutant was unaffected in plant attachment or colonization. Tafi, cellulose synthesis, and O-antigen capsule, all of which contribute to attachment and colonization of plants, are regulated by AgfD, suggesting that AgfD is a key regulator for survival outside of hosts of Salmonella spp. The cellulose biosynthesis regulator adrA mutant was not affected in the ability to attach to or colonize plants; however, promoter probe assays revealed expression by cells attached to alfalfa sprouts. Furthermore, quantitative reverse-transcriptase polymerase chain reaction revealed differential expression of agfD and adrA between planktonic and plant-attached cells. In addition, there was no correlation among mutants between biofilm formation in culture and attachment to plants. Outside of animal hosts, S. enterica appears to rely on an arsenal of adhesins to persist on plants, which can act as vectors and perpetuate public health concerns.
The American Phytopathological Society, 2007