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Infection and Immunity, July 2006, p. 3742-3755, Vol. 74, No. 7
0019-9567/06/$08.00+0     doi:10.1128/IAI.00402-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Molecular and Functional Characterization of a ToxR-Regulated Lipoprotein from a Clinical Isolate of Aeromonas hydrophila

Lakshmi Pillai, Jian Sha, Tatiana E. Erova, Amin A. Fadl, Bijay K. Khajanchi, and Ashok K. Chopra*

Department of Microbiology and Immunology, University of Texas Medical Branch, Galveston, Texas 77555-1070

Received 13 March 2006/ Returned for modification 10 April 2006/ Accepted 18 April 2006

Human diseases caused by species of Aeromonas have been classified into two major groups: septicemia and gastroenteritis. In this study, we reported the molecular and functional characterization of a new virulence factor, ToxR-regulated lipoprotein, or TagA, from a diarrheal isolate, SSU, of Aeromonas hydrophila. The tagA gene of A. hydrophila exhibited 60% identity with that of a recently identified stcE gene from Escherichia coli O157:H7, which encoded a protein (StcE) that provided serum resistance to the bacterium and prevented erythrocyte lysis by controlling classical pathway of complement activation by cleaving the complement C1-esterase inhibitor (C1-INH). We purified A. hydrophila TagA as a histidine-tagged fusion protein (rTagA) from E. coli DE3 strain using a T7 promoter-based pET30 expression vector and nickel affinity column chromatography. rTagA cleaved C1-INH in a time-dependent manner. The tagA isogenic mutant of A. hydrophila, unlike its corresponding wild-type (WT) or the complemented strain, was unable to cleave C1-INH, which is required to potentiate the C1-INH-mediated lysis of host and bacterial cells. We indeed demonstrated colocalization of C1-INH and TagA on the bacterial surface by confocal fluorescence microscopy, which ultimately resulted in increased serum resistance of the WT bacterium. Likewise, we delineated the role of TagA in contributing to the enhanced ability of C1-INH to inhibit the classical complement-mediated lysis of erythrocytes. Importantly, we provided evidence that the tagA mutant was significantly less virulent in a mouse model of infection (60%) than the WT bacterium at two 50% lethal doses, which resulted in 100% mortality within 48 h. Taken together, our data provided new information on the role of TagA as a virulence factor in bacterial pathogenesis. This is the first report of TagA characterization from any species of Aeromonas.

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

Editor: J. T. Barbieri

Infection and Immunity, July 2006, p. 3742-3755, Vol. 74, No. 7
0019-9567/06/$08.00+0     doi:10.1128/IAI.00402-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



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