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Infect. Immun., May 1996, 1694-1705, Vol 64, No. 5
J De Rycke, P Mazars, JP Nougayrede, C Tasca, M Boury, F Herault, A Valette and E Oswald
The cytopathic effect (CPE) of Escherichia coli producing cytotoxic
necrotizing factor type 1 (CNF1) was investigated by using a human
epithelial cell (HeLa) model of infection with CNF1-producing E. coli
BM2-1. This strain was shown to bind loosely, but massively, to HeLa cells.
A 4-h interaction between bacteria and eukaryotic cells triggered the
delayed appearance of a progressive dose-dependent CPE characterized by (i)
intense swelling of cells accompanied by the formation of a dense network
of actin stress fibers, (ii) inhibition of cell division due to a complete
block in the G2 phase of the cell cycle, and (iii) nucleus swelling and
chromatin fragmentation. These alterations resulted in cell death starting
about 5 days after interaction. The absence of multinucleation clearly
distinguished the CPE from the effect produced by cell-free culture
supernatants of infected cells nor prevented by a CNF1-neutralizing
antiserum. Pathogenicity was completely abolished after Tn5::phoA insertion
mutagenesis in the cnf-1 structural gene but not restored by trans
complementation with a recombinant plasmid containing intact cnf-1 and its
promoter. These results suggest that a gene downstream of cnf-1, essential
to the induction of the CPE, was affected by the mutation. On the other
hand, transformation of the wild-type strain BM2-1 with the same
recombinant plasmid leads to a significant increase in both CNF1 activity
and CPE, demonstrating the direct contribution of CNF1 to the CPE. In
conclusion, the pathogenicity of E. coli BM2-1 for HeLa cells results from
a complex interaction involving cnf-1 and associated genes and possibly
requiring a preliminary step of binding of bacterial organisms to target
cells.
Copyright © 1996, American Society for Microbiology
Mitotic block and delayed lethality in HeLa epithelial cells exposed to Escherichia coli BM2-1 producing cytotoxic necrotizing factor type 1
Laboratoire Associe de Microbiologie Moleculaire, Institut National de la Recherche Agronomique, Ecole Nationale Veterinaire, Toulouse, France.
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