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

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 aggregat...

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Bibliographic Details
Published in:Infection and Immunity 2008-03, Vol.76 (3), p.1048-1058
Main Authors: White, A.P, Gibson, D.L, Grassl, G.A, Kay, W.W, Finlay, B.B, Vallance, B.A, Surette, M.G
Format: Article
Language:English
Subjects:
Animal Structures - microbiology
Animals
Anti-Bacterial Agents - pharmacology
Bacterial Adhesion - physiology
Bacterial Infections
Colony Count, Microbial
Female
Fimbriae Proteins - genetics
Fimbriae, Bacterial - physiology
Gene Deletion
Genes, Reporter
Luciferases - genetics
Luciferases - metabolism
Luminescence
Mice
Mice, Inbred C57BL
Salmonella enterica
Salmonella Infections, Animal - microbiology
Salmonella typhimurium - drug effects
Salmonella typhimurium - pathogenicity
Salmonella typhimurium - physiology
Sodium Hypochlorite - pharmacology
Virulence
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Summary: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 ΔagfA 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.
ISSN:0019-9567
1098-5522
DOI:10.1128/IAI.01383-07