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Infection and Immunity, November 2008, p. 5072-5081, Vol. 76, No. 11
0019-9567/08/$08.00+0 doi:10.1128/IAI.00677-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.
CadA Negatively Regulates Escherichia coli O157:H7 Adherence and Intestinal Colonization
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Roberto C. Vazquez-Juarez,3,
Jeeba A. Kuriakose,2
David A. Rasko,4
Jennifer M. Ritchie,5
Melissa M. Kendall,4
Terry M. Slater,1
Mala Sinha,6
Bruce A. Luxon,6
Vsevolod L. Popov,2
Matthew K. Waldor,5
Vanessa Sperandio,4 and
Alfredo G. Torres1,2*
Department of Microbiology and Immunology,1 Department of Pathology,2 Bioinformatics Program, University of Texas Medical Branch, Galveston, Texas 77555-1070,6 Departamento de Patología Marina, Centro de Investigaciones Biológicas del Noroeste, La Paz, B.C.S. 23000, México,3 Department of Microbiology, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9048,4 Channing Laboratory, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 021155
Received 30 May 2008/ Returned for modification 27 June 2008/ Accepted 19 August 2008
Adherence of pathogenic Escherichia coli strains to intestinal epithelia is essential for infection. For enterohemorrhagic E. coli (EHEC) serotype O157:H7, we have previously demonstrated that multiple factors govern this pathogen's adherence to HeLa cells (A. G. Torres and J. B. Kaper, Infect. Immun. 71:4985-4995, 2003). One of these factors is CadA, a lysine decarboxylase, and this protein has been proposed to negatively regulate virulence in several enteric pathogens. In the case of EHEC strains, CadA modulates expression of the intimin, an outer membrane adhesin involved in pathogenesis. Here, we inactivated cadA in O157:H7 strain 86-24 to investigate the role of this gene in EHEC adhesion to tissue-cultured monolayers, global gene expression patterns, and colonization of the infant rabbit intestine. The cadA mutant did not possess lysine decarboxylation activity and was hyperadherent to tissue-cultured cells. Adherence of the cadA mutant was nearly twofold greater than that of the wild type, and the adherence phenotype was independent of pH, lysine, or cadaverine in the media. Additionally, complementation of the cadA defect reduced adherence back to wild-type levels, and it was found that the mutation affected the expression of the intimin protein. Disruption of the eae gene (intimin-encoding gene) in the cadA mutant significantly reduced its adherence to tissue-cultured cells. However, adherence of the cadA eae double mutant was greater than that of an 86-24 eae mutant, suggesting that the enhanced adherence of the cadA mutant is not entirely attributable to enhanced expression of intimin in this background. Gene array analysis revealed that the cadA mutation significantly altered EHEC gene expression patterns; expression of 1,332 genes was downregulated and that of 132 genes was upregulated in the mutant compared to the wild-type strain. Interestingly, the gene expression variation shows an EHEC-biased gene alteration including intergenic regions. Two putative adhesins, flagella and F9 fimbria, were upregulated in the cadA mutant, suggestive of their association with adherence in the absence of the Cad regulatory mechanism. In the infant rabbit model, the cadA mutant outcompeted the wild-type strain in the ileum but not in the cecum or mid-colon, raising the possibility that CadA negatively regulates EHEC pathogenicity in a tissue-specific fashion.
* Corresponding author. Mailing address: Department of Microbiology and Immunology, University of Texas Medical Branch, Galveston, TX 77555-1070. Phone: (409) 747-0189. Fax: (409) 747-6869. E-mail: altorres{at}utmb.edu
Published ahead of print on 15 September 2008.
Supplemental material for this article may be found at http://iai.asm.org/.
In memory of Dr. Vazquez-Juarez, who initiated this study in the Torres lab.
Infection and Immunity, November 2008, p. 5072-5081, Vol. 76, No. 11
0019-9567/08/$08.00+0 doi:10.1128/IAI.00677-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.
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