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Category: Microbial Genetics and Molecular Biology; Bacterial Pathogenesis
Holistic Perspective on the Escherichia coli Hemolysin, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555818340/9781555810825_Chap23-1.gif /docserver/preview/fulltext/10.1128/9781555818340/9781555810825_Chap23-2.gifAbstract:
This chapter reviews the knowledge of the prototype of the RTX family of pore-forming toxins, the Escherichia coli hemolysin, and proposes that new efforts be made to study the significance and roles of the exotoxins, together with those of endotoxins, as an integrated synergistic system of multiple virulence factors. The fundamental approach taken by biochemists and cell biologists interested in understanding the role in pathogenesis of a bacterial virulence factor such as an exoprotein has been to purify the exoprotein and observe its activity on different substrates, cells, and hosts. The RTX-associated diseases include pertussis, juvenile periodontitis, pneumonia, urinary tract infections, and wound infections. The epidemiological evidence for an association between RTX toxin production and isolates that cause disease is strong for all of the organisms except E. colii, Morganella morganii, and Proteus vulgaris. The solubilization of hemolysin aggregates by a chaotropic agent such as urea causes an increase in the specific lytic activity of the hemolysin. The erythrocytes transform into echinocytes, in which gross cytoskeletal or membrane irregularities result in rounding of the cell and the formation of multiple teardrop-shaped projections from the cell surface. The cellular transformation is similar to that caused by the treatment of erthrocytes by a calcium ionophore. The motivation for covering the older literature in the chapter is to stimulate thought, experimentation, and discussion about the significance of the ever-present lipopolysaccharide (LPS) molecules on the structure and activity of the E. coli hemolysin.
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After a 5-min treatment with the E. coli hemolysin, sheep erythrocytes were fixed and visualized by scanning electron microscopy ( 30 ). The photograph shows the loss of the concave cellular structure typical of erythrocytes and the formation of multiple teardrop-shaped projections from the cell surface. Bar, 2 μm. The photograph was the gift of Sally Jorgensen, University of Minnesota.
After a 5-min treatment with the E. coli hemolysin, sheep erythrocytes were fixed and visualized by scanning electron microscopy ( 30 ). The photograph shows the loss of the concave cellular structure typical of erythrocytes and the formation of multiple teardrop-shaped projections from the cell surface. Bar, 2 μm. The photograph was the gift of Sally Jorgensen, University of Minnesota.
Selected features of toxins from the RTX toxin branch of the RTX exoprotein family
a The predicted pi, based on the predicted amino acid sequence of the toxin gene product.
b PMNs, polymorphonuclear leukocytes.
c A weak hemolytic activity is observed.
d No hemolytic activity is observed.
Selected features of toxins from the RTX toxin branch of the RTX exoprotein family
a The predicted pi, based on the predicted amino acid sequence of the toxin gene product.
b PMNs, polymorphonuclear leukocytes.
c A weak hemolytic activity is observed.
d No hemolytic activity is observed.