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Infection and Immunity, March 2008, p. 1048-1058, Vol. 76, No. 3
0019-9567/08/$08.00+0     doi:10.1128/IAI.01383-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Aggregation via the Red, Dry, and Rough Morphotype Is Not a Virulence Adaptation in Salmonella enterica Serovar Typhimurium{triangledown}

A. P. White,1 D. L. Gibson,2,{dagger} G. A. Grassl,3,{dagger} W. W. Kay,4 B. B. Finlay,3,5 B. A. Vallance,2 and M. G. Surette1*

Department of Microbiology and Infectious Diseases, University of Calgary, Calgary, Alberta T2N 4N1, Canada,1 Division of Gastroenterology, BC's Children's Hospital, University of British Columbia, Vancouver BC V5Z 4H4, Canada,2 Michael Smith Laboratories, University of British Columbia, Vancouver BC V6T 1Z4, Canada,3 Department of Biochemistry and Microbiology, University of Victoria, Victoria BC V8W 3P6, Canada,4 Department of Microbiology and Immunology, University of British Columbia, Vancouver BC V6T 1Z4, Canada5

Received 16 October 2007/ Returned for modification 19 November 2007/ Accepted 19 December 2007

The Salmonella rdar (red, dry, and rough) morphotype is an aggregative and resistant physiology that has been linked to survival in nutrient-limited environments. Growth of Salmonella enterica serovar Typhimurium was analyzed in a variety of nutrient-limiting conditions to determine whether aggregation would occur at low cell densities and whether the rdar morphotype was involved in this process. The resulting cultures consisted of two populations of cells, aggregated and nonaggregated, 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 nonaggregative {Delta}agfA cells outcompeted rdar-positive wild-type 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.

* Corresponding author. Mailing address: Department of Microbiology and Infectious Diseases, University of Calgary, Faculty of Medicine, 268 Heritage Medical Research Building, 3330 Hospital Drive NW, Calgary, Alberta T2N 4N1, Canada. Phone: (403) 220-2744. Fax: (403) 270-2772. E-mail: surette{at}ucalgary.ca

{triangledown} Published ahead of print on 14 January 2008.

Editor: A. J. Bäumler

{dagger} These authors contributed equally to this work.

Infection and Immunity, March 2008, p. 1048-1058, Vol. 76, No. 3
0019-9567/08/$08.00+0     doi:10.1128/IAI.01383-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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