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J Med Microbiol 55 (2006), 669-675; DOI: 10.1099/jmm.0.46344-0
© 2006 Society for General Microbiology
ISSN 1473-5644

Basis for N-acetyllactosamine-mediated inhibition of enteropathogenic Escherichia coli localized adherence

Romney M. Hyland1, Thomas P. Griener1, George L. Mulvey1, Pavel I. Kitov2, Om P. Srivastava3, Paola Marcato4 and Glen D. Armstrong1

1 Department of Microbiology and Infectious Diseases, Faculty of Medicine, University of Calgary, 3330 Hospital Drive, NW, Calgary, AB, T2N 4N1, Canada

2 Department of Chemistry, University of Alberta, Edmonton, AB, T6G 2G2, Canada

3 Alberta Research Council, 250 Karl Clark Road, Edmonton, AB, T6N 1E4, Canada

4 Department of Medical Microbiology and Immunology, University of Alberta, Edmonton, AB, T6G 2H7, Canada

Correspondence
Glen D. Armstrong
glen.armstrong{at}ucalgary.ca

Received 23 September 2005
Accepted 19 February 2006

In a previous article, the authors reported that exposing wild-type enteropathogenic Escherichia coli (EPEC) to chemically synthesized N-acetyllactosamine glycosides covalently coupled to BSA (LacNAc–BSA) inhibited localized adherence (LA) by these organisms and also caused them to lose their bundle-forming pili (BFP), the filamentous surface appendages responsible for their LA phenotype. This effect has now been further investigated by screening a panel of LacNAc–BSA-related glycosides for their ability to inhibit EPEC LA, which revealed that LacNAc–BSA retained its status as the most effective inhibitor of EPEC LA. It was also shown that LacNAc–BSA did not cause the loss of BFP in an EPEC strain containing a non-polar mutation in the bfpF gene and, as a consequence, unable to retract its BFP. LacNAc–BSA also effectively inhibited LA of the bfpF mutant EPEC. Taken together, these observations suggest that, as well as triggering BfpF-mediated BFP retraction, LacNAc–BSA likely functions as a competitive inhibitor of EPEC binding to LacNAc-related receptors on host cells. Moreover, transmission electron microscopy revealed that LacNAc conjugated to gold nanoparticles bound specifically to BFP. This observation indicated that either the major BFP structural subunit (BfpA) itself or, possibly, an accessory protein co-assembled with BfpA into the BFP filaments, contains a LacNAc-specific EPEC adhesin. The results suggest a mechanism whereby the initial binding of EPEC to LacNAc-like receptors on host cells triggers BfpF-mediated BFP retraction. This could then expedite the intimate adherence phase of the multi-step EPEC colonization process by drawing the organisms closer to the host-cell plasma membrane.

Abbreviations: BFP, bundle-forming pili; EPEC, enteropathogenic Escherichia coli; LA, localized adherence; LacNAc, N-acetyllactosamine; MBP, maltose binding protein; Pk, {alpha}Gal(1,4)ßGal(1,4)ßGlc.




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