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Infect. Immun. doi:10.1128/IAI.01383-07
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Aggregation via the rdar morphotype is not a virulence adaptation in Salmonella enterica serovar Typhimurium

Department of Microbiology and Infectious Diseases, University of Calgary, Calgary, Alberta, T2N 4N1, Canada; Division of Gastroenterology, B.C.'s Children's Hospital, University of British Columbia, Vancouver, BC, V5Z 4H4, Canada; Michael Smith Laboratories, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada; Department of Biochemistry and Microbiology, University of Victoria, Victoria, BC, V8W 3P6, Canada; Department of Microbiology and Immunology, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada

^* To whom correspondence should be addressed. Email: surette{at}ucalgary.ca.

	Abstract

The Salmonella rdar morphotype is an aggregative and resistant physiology that has been linked to survival in nutrient-limited environments. Growth of S. enterica serovar Typhimurium was analyzed in a variety of nutrient-limiting conditions to determine if aggregation would occur at low cell densities and if the rdar morphotype was involved in this process. The resulting cultures consisted of two populations of cells, aggregated and non-aggregated, with the aggregated cells preferentially displaying rdar morphotype gene expression. The two groups of cells could be separated based on the principle that aggregated cells were producing greater amounts of thin aggregative fimbriae (Tafi or curli). In addition, the aggregated cells retained some physiological characteristics of the rdar morphotype, such as increased resistance to sodium hypochlorite. Competitive infection experiments in mice showed that non-aggregative agfA cells out-competed rdar-positive wt cells in all tissues analyzed, indicating that aggregation via the rdar morphotype was not a virulence adaptation in Salmonella enterica serovar Typhimurium. Furthermore, in vivo imaging experiments showed that Tafi genes were not expressed during infection, but were expressed once Salmonella was passed out of the mice into the feces. We hypothesize that the primary role of the rdar morphotype is to enhance Salmonella survival outside the host, thereby aiding in transmission.