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Updated: Aug 11, 2026
Chronic Salmonella Infected Mouse Model
Published on: May 31, 2010
SifA permits survival and replication of Salmonella typhimurium in murine macrophages
J H Brumell1, C M Rosenberger, G T Gotto
1Department of Biochemistry, University of British Columbia, Vancouver, Canada.
Abstract:
SifA was originally identified as a virulence factor required for formation of Salmonella-induced filaments (Sifs), elongated tubules rich in lysosomal glycoproteins that extend from the Salmonella-containing vacuole in infected epithelial cells. Here, we demonstrate that deletion mutants of ssaR, a component of the SPI-2 type III secretion system, do not form Sifs in HeLa epithelial cells. This suggests that SifA is a translocated effector of this system, acting within host cells to form Sifs. In support of this hypothesis, transfection of HeLa cells with a vector encoding SifA fused to the green fluorescent protein caused extensive vacuolation of LAMP-1-positive compartments. Filamentous tubules that closely resembled Sifs were also observed in transfected cells, demonstrating that SifA is sufficient to initiate alteration of host cell endosomal structures. deltasifA mutants were impaired in their ability to survive/replicate in RAW 264.7 murine macrophages, a phenotype similar to ssaR mutants. Our findings suggest that SifA is an effector of the SPI-2 type III secretion system and allows colonization of murine macrophages, the host niche exploited during systemic phases of disease in these animals. A family of SifA-related proteins and their importance to Salmonella pathogenesis is also discussed.
Insights
Salmonella SifA protein is crucial for forming Salmonella-induced filaments (Sifs) and colonizing host cells. It acts as an effector of the SPI-2 type III secretion system, enabling bacterial survival in macrophages.
Area of Science:
- Microbiology
- Cell Biology
- Pathogenesis
Background:
- Salmonella-induced filaments (Sifs) are structures that extend from the Salmonella-containing vacuole in infected cells.
- SifA was initially identified as a virulence factor essential for Sif formation.
Purpose of the Study:
- To investigate the role of SifA in Salmonella pathogenesis.
- To determine if SifA is an effector of the SPI-2 type III secretion system.
- To elucidate the function of SifA in host cell manipulation and bacterial survival.
Main Methods:
- Deletion mutagenesis of ssaR and sifA genes in Salmonella.
- Transfection of HeLa cells with SifA-green fluorescent protein fusion constructs.
- Analysis of Sif formation and host cell vacuolation using microscopy.
- Assessment of bacterial survival and replication in RAW 264.7 murine macrophages.
Main Results:
- Deletion mutants of ssaR, a SPI-2 type III secretion system component, failed to form Sifs.
- Transfection with SifA induced extensive vacuolation of LAMP-1-positive compartments and formation of Sif-like tubules.
- SifA alone was sufficient to initiate alterations in host cell endosomal structures.
- Mutants lacking SifA (deltasifA) showed impaired survival and replication in murine macrophages, similar to ssaR mutants.
Conclusions:
- SifA is a translocated effector of the SPI-2 type III secretion system.
- SifA mediates the formation of Sifs and plays a critical role in Salmonella colonization of murine macrophages.
- SifA is essential for Salmonella pathogenesis during systemic infection phases.
