SifA permits survival and replication of Salmonella typhimurium in murine macrophages

Cell Microbiol. 2001 Feb;3(2):75-84. doi: 10.1046/j.1462-5822.2001.00087.x.


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.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Antigens, CD / metabolism
  • Bacterial Proteins / metabolism*
  • Cell Division
  • Epithelial Cells / microbiology
  • Glycoproteins / genetics
  • HeLa Cells
  • Humans
  • Lysosome-Associated Membrane Glycoproteins
  • Macrophages / microbiology*
  • Membrane Glycoproteins / metabolism
  • Molecular Sequence Data
  • Salmonella typhimurium / pathogenicity*
  • Sequence Homology, Amino Acid


  • Antigens, CD
  • Bacterial Proteins
  • Glycoproteins
  • Lysosome-Associated Membrane Glycoproteins
  • Membrane Glycoproteins
  • SifA protein, Salmonella