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Infect. Immun., Jul 1997, 2759-2764, Vol 65, No. 7
DR Cue and PP Cleary
The ability of Streptococcus pyogenes to invade human epithelial cells has
been suggested to be an important contributing factor to the bacterium's
ability to cause severe, invasive infections. We know little, however, of
the mechanism underlying intracellular invasion by this organism. In this
study, we demonstrate that the invasion of cultured human epithelial cells
by a serotype M1 strain of S. pyogenes (strain 90-226) is stimulated over
50-fold by the addition of fetal calf serum (FCS) to the cell culture
medium (RPMI medium). Purified human fibrinogen and peptides containing the
sequence Arg-Gly-Asp (RGD) were also found to promote bacterial invasion of
cultured cells. Experiments that demonstrate that the agonists stimulate
invasion by interacting with bacterial cells are described. Invasion
stimulation did not appear to involve de novo synthesis of a bacterial
protein, as FCS and fibrinogen stimulated invasion in the presence of
chloramphenicol. Although the agonists stimulated adherence by up to
threefold, strain 90-226 efficiently adhered to cultured cells in
unsupplemented RPMI medium. The invasion index (the number of internalized
CFU/the number of adherent CFU) of strain 90-226 was increased 10- to
25-fold by the addition of the agonists. Postinternalization survival of
bacteria was unaffected by fibrinogen or FCS. Thus, the agonistic factors
affect the efficiency by which adherent bacteria are internalized by
epithelial cells.
Copyright © 1997, American Society for Microbiology
High-frequency invasion of epithelial cells by Streptococcus pyogenes can be activated by fibrinogen and peptides containing the sequence RGD
Department of Microbiology, University of Minnesota Medical School, Minneapolis 55455, USA.
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