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Infection and Immunity, August 2005, p. 4753-4765, Vol. 73, No. 8
0019-9567/05/$08.00+0     doi:10.1128/IAI.73.8.4753-4765.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Identification and Characterization of the Locus for Diffuse Adherence, Which Encodes a Novel Afimbrial Adhesin Found in Atypical Enteropathogenic Escherichia coli

Isabel C. A. Scaletsky,1 Jane Michalski,2* Alfredo G. Torres,3 Michelle V. Dulguer,1 and James B. Kaper2

Department of Microbiology and Immunology, Universidade Federal de São Paulo, São Paulo, Brazil 04023-062,1 Department of Microbiology and Immunology and Center for Vaccine Development, University of Maryland, Baltimore, Maryland 21201,2 Department of Microbiology and Immunology and Department of Pathology, University of Texas Medical Branch, Galveston, Texas 77555-10703

Received 6 January 2005/ Returned for modification 11 February 2005/ Accepted 4 April 2005

The O26 serogroup of enteropathogenic Escherichia coli (EPEC) is one of the serogroups most frequently implicated in infant diarrhea and is also common among enterohemorrhagic E. coli (EHEC) strains. The most common O26 strains belong to EPEC/EHEC serotype O26:H11 and are generally Shiga toxin (Stx) positive. Stx-negative E. coli strains that are negative for the EPEC EAF plasmid and bundle-forming pilus (Bfp) are classified as atypical EPEC. Here, we report a novel adhesin present in an stx-negative bfpA-negative atypical EPEC O26:H11 strain isolated from an infant with diarrhea. A cloned 15-kb genomic region from this strain, designated the locus for diffuse adherence (lda), confers diffuse adherence on HEp-2 cells when expressed in E. coli K-12. Sequence analysis of lda revealed a G+C content of 46.8% and 15 open reading frames sharing homology with the E. coli K88 fae and CS31A clp fimbrial operons. The lda region is part of a putative 26-kb genomic island inserted into the proP gene of the E. coli chromosome. Hybridization studies have demonstrated the prevalence of the minor structural subunit gene, ldaH, across E. coli serogroups O5, O26, O111, and O145. A second plasmid-encoded factor that contributed to the Hep-2 adherence of this strain was also identified but was not characterized. Null mutations that abolish adherence to HEp-2 cells can be restored by plasmid complementation. Antiserum raised against the major structural subunit, LdaG, recognizes a 25-kDa protein from crude heat-extracted protein preparations and inhibits the adherence of the E. coli DH5{alpha} lda+ clone to HEp-2 cells. Electron microscopy revealed a nonfimbrial structure surrounding the bacterial cell.

* Corresponding author. Mailing address: University of Maryland, Baltimore, 685 W. Baltimore St., Baltimore, MD 21201. Phone: (410) 706-2493. Fax: (410) 706-0182. E-mail: jmichals{at}medicine.umaryland.edu.

Editor: A. D. O'Brien

Infection and Immunity, August 2005, p. 4753-4765, Vol. 73, No. 8
0019-9567/05/$08.00+0     doi:10.1128/IAI.73.8.4753-4765.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.



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