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Infection and Immunity, April 2003, p. 1725-1732, Vol. 71, No. 4
0019-9567/03/$08.00+0     DOI: 10.1128/IAI.71.4.1725-1732.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Differential Modulation by Ca2+ of Type III Secretion of Diffusely Adhering Enteropathogenic Escherichia coli

Tina Ide, Silke Michgehl, Sabine Knappstein, Gerhard Heusipp, and M. Alexander Schmidt*

Institut für Infektiologie-Zentrum für Molekularbiologie der Entzündung (ZMBE), Westfälische Wilhelms-Universität Münster, Münster, Germany

Received 12 June 2002/ Returned for modification 26 August 2002/ Accepted 23 December 2002

Enteropathogenic Escherichia coli (EPEC) strains are a common cause of persistent diarrhea among infants, primarily in developing countries. The pathogenicity of EPEC is associated with the expression and secretion of bacterial proteins encoded by the chromosomal locus of enterocyte effacement (LEE). The LEE-encoded type III-secreted proteins EspA, EspB, and EspD are part of a molecular syringe, which is used by EPEC to translocate effector proteins directly into the cytoplasm of host cells. The type III-secreted translocated intimin receptor (Tir) protein is thought to be delivered by an Esp-dependent mechanism into the host cell, and this is followed by insertion into the host plasma membrane, where the protein serves as the receptor for intimin, an afimbrial bacterial adhesin. Type III secretion is subject to environmental regulation, and secretion can be induced in vitro by growing bacteria in cell culture medium. In this study we found that Ca2+ is involved in the regulation of type III secretion both in classical locally adherent EPEC and in atypical diffusely adherent EPEC. Interestingly, we observed contrasting secretion of Esp proteins and Tir in response to Ca2+. While the secretion of Tir is clearly enhanced and the protein is integrated into HeLa membranes under calcium chelation conditions, Esp secretion is strongly reduced under these conditions. These data suggest that under Ca2+-depleted conditions Tir might be secreted into the medium and integrated into host membranes by an Esp-independent mechanism, without the need for a functional type III translocation machinery.

* Corresponding author. Mailing address: Institut für Infektiologie-Zentrum für Molekularbiologie der Entzündung (ZMBE), Von-Esmarch-Str. 56, D-48149 Münster, Germany. Phone: 49 251 835 64 66. Fax: 49 251 835 64 67. E-mail: infekt{at}uni-muenster.de.

Editor: V. J. DiRita

Infection and Immunity, April 2003, p. 1725-1732, Vol. 71, No. 4
0019-9567/03/$08.00+0     DOI: 10.1128/IAI.71.4.1725-1732.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.



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