Release of the Type I Secreted Alpha-Haemolysin via Outer Membrane Vesicles From Escherichia Coli

Mol Microbiol. 2006 Jan;59(1):99-112. doi: 10.1111/j.1365-2958.2005.04938.x.


The alpha-haemolysin is an important virulence factor commonly expressed by extraintestinal pathogenic Escherichia coli. The secretion of the alpha-haemolysin is mediated by the type I secretion system and the toxin reaches the extracellular space without the formation of periplasmic intermediates presumably in a soluble form. Surprisingly, we found that a fraction of this type I secreted protein is located within outer membrane vesicles (OMVs) that are released by the bacteria. The alpha-haemolysin appeared very tightly associated with the OMVs as judged by dissociation assays and proteinase susceptibility tests. The alpha-haemolysin in OMVs was cytotoxically active and caused lysis of red blood cells. The OMVs containing the alpha-haemolysin were distinct from the OMVs not containing alpha-haemolysin, showing a lower density. Furthermore, they differed in protein composition and one component of the type I secretion system, the TolC protein, was found in the lower density vesicles. Studies of natural isolates of E. coli demonstrated that the localization of alpha-haemolysin in OMVs is a common feature among haemolytic strains. We propose an alternative pathway for the transport of the type I secreted alpha-haemolysin from the bacteria to the host cells during bacterial infections.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Outer Membrane Proteins / metabolism
  • Cell Membrane / metabolism*
  • Cytoplasmic Vesicles / chemistry
  • Cytoplasmic Vesicles / metabolism
  • Cytoplasmic Vesicles / ultrastructure
  • Escherichia coli / cytology
  • Escherichia coli / metabolism*
  • Escherichia coli / pathogenicity
  • Escherichia coli Infections
  • Escherichia coli Proteins / metabolism
  • Fatty Acids / metabolism
  • HeLa Cells
  • Hemolysin Proteins / metabolism*
  • Humans
  • Membrane Transport Proteins


  • Bacterial Outer Membrane Proteins
  • Escherichia coli Proteins
  • Fatty Acids
  • Hemolysin Proteins
  • Membrane Transport Proteins
  • tolC protein, E coli