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Journal of Bacteriology, May 2009, p. 3095-3107, Vol. 191, No. 9
0021-9193/09/$08.00+0     doi:10.1128/JB.00005-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Surface-Expressed Enolase Contributes to the Pathogenesis of Clinical Isolate SSU of Aeromonas hydrophila{triangledown}

Jian Sha,1,3 Tatiana E. Erova,1,3 Rebecca A. Alyea,1,3 Shaofei Wang,1,3 Juan P. Olano,2,3 Vijay Pancholi,4 and Ashok K. Chopra1,3*

Departments of Microbiology and Immunology,1 Pathology, Institute of Human Infections and Immunity,2 Sealy Center for Vaccine Development, University of Texas Medical Branch, Galveston, Texas 77555,3 Ohio State University College, Columbus, Ohio 432104

Received 2 January 2009/ Accepted 17 February 2009

In this study, we demonstrated that the surface-expressed enolase from diarrheal isolate SSU of Aeromonas hydrophila bound to human plasminogen and facilitated the latter's tissue-type plasminogen activator-mediated activation to plasmin. The bacterial surface-bound plasmin was more resistant to the action of its specific physiological inhibitor, the antiprotease {alpha}2-antiplasmin. We found that immunization of mice with purified recombinant enolase significantly protected the animals against a lethal challenge dose of wild-type (WT) A. hydrophila. Minimal histological changes were noted in organs from mice immunized with enolase and then challenged with WT bacteria compared to severe pathological changes found in the infected and nonimmunized group of animals. This correlated with the smaller bacterial load of WT bacteria in the livers and spleens of enolase-immunized mice than that found in the nonimmunized controls. We also showed that the enolase gene could potentially be important for the viability of A. hydrophila SSU as we could delete the chromosomal copy of the enolase gene only when another copy of the targeted gene was supplied in trans. By site-directed mutagenesis, we altered five lysine residues located at positions 343, 394, 420, 427, and 430 of enolase in A. hydrophila SSU; the mutated forms of enolase were hyperexpressed in Escherichia coli, and the proteins were purified. Our results indicated that lysine residues at positions 420 and 427 of enolase were crucial in plasminogen-binding activity. We also identified a stretch of amino acid residues (252FYDAEKKEY260) in the A. hydrophila SSU enolase involved in plasminogen binding. To our knowledge, this is the first report of the direct involvement of surface-expressed enolase in the pathogenesis of A. hydrophila SSU infections and of any gram-negative bacteria in general.

* Corresponding author. Mailing address: Department of Microbiology and Immunology, 301 University Blvd., Medical Research Building, UTMB, Galveston, TX 77555-1070. Phone: (409) 747-0578. Fax: (409) 747-6869. E-mail: achopra{at}utmb.edu

{triangledown} Published ahead of print on 6 March 2009.

Journal of Bacteriology, May 2009, p. 3095-3107, Vol. 191, No. 9
0021-9193/09/$08.00+0     doi:10.1128/JB.00005-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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