Congo red binding phenotype is associated with hemin binding and increased infectivity of Shigella flexneri in the HeLa cell model

Abstract

Wild-type isolates of Shigella flexneri bind the dye Congo red from solid media, thus producing red (Crb+) colonies. Mutants which fail to bind the dye produce white colonies (Crb-) and are avirulent in a variety of systems. In S. flexneri the ability to bind Congo red correlates with the ability to bind hemin and protoporphyrin IX. Binding of hemin by Crb+ S. flexneri was observed both in solid media and in liquid assays. Results of competition experiments suggest that Congo red and hemin bind to the same site on the bacterial cell and are retained on the cell surface. Binding of hemin by Crb+ S. flexneri is independent of hemin transport since both Crb+ and Crb- cells can utilize hemin as a sole source of iron. Both Crb- and Crb- organisms were able to grow in HeLa cell lysates, indicating that the gene(s) that is responsible for Congo red binding does not play a role in the acquisition of intracellular heme iron. By using the HeLa cell invasion system, the effect of hemin prebinding on the invasiveness of Crb+ S. flexneri was determined. Crb+ cells which had prebound hemin exhibited increased invasiveness, indicating a possible role for the crb gene product in the initial stages of invasion by S. flexneri.

Quelling the red menace: haem capture by bacteria

“…Although haem binding has long been recognized as a virulence marker (Perry and Brubaker, 1979;Kay et aL, 1985;Daskaleros and Payne, 1987;Stugard et aL, 1989;Perry et aL, 1993), the molecular basis for this trait is unknown. The dissociation between this phenotype and the ability to transport haem (Payne, 1989) suggests that the adsorbance of haem to the bacterial surface involves proteins not engaged in haem uptake.…”

Iron and virulence in Shigella

“…The components of the haem-iron transport system have not been elucidated. However, it has been noted that wild-type shigeliae are able to bind relatively large amounts of haemin at the celi surface (Crb+ phenotype) (Daskaleros and Payne, 1987). The haemin is bound to a plasmid-encoded, cell-surface protein with an approximate molecular weight of 100000 (Stugard et ai., 1989).…”

“…The ability to bind haemin (or the dye Congo red) at the ceil surface does correlate with virulence, however (Payne and Finkeistein, 1977). Crb" mutants fail to invade and appear to be defective in an early step in the invasion process (Daskaleros and Payne, 1987;'Maurelii etai., 1984;Payne and Finkeistein, 1977). The effect of haemin on invasion was tested, and the presence of surface-bound haemin greatly enhanced the infectivity of Shigeila for tissue-culture ceils (Daskaieros and Payne, 1987).…”

Utilization of haem compounds by Aeromonas salmonicida

“…The A-layer is also capable of binding the aromatic dye, congo red and the haem compounds haeniin, protoporphyrin IX and haematoporphyrin (Ishiguro, Ainsworth, Trust & Kay 1985;Kay, Phipps, Ishiguro & Trust 1985). The association of congo red binding and virulence has been described for a number of pathogens including Escherichia coli, Shigella flexneri and Yersinia enterocolitica (Stugard, Daskaleros & Payne 1989;Pripic, Robins-Browne & Davey 19(S3) and is often associated with the ability to use haem as a source of iron (Daskaleros & Payne 1987;Deneer & Potter 1989). The aim of this work was to study the ability of A. salmonicida to utilize haem compounds as sole sources of iron under conditions of iron-restriction and to investigate the role of the A-layer protein in this process.…”