Role of new virulence mechanisms/factors (type 3 secretion system and TOX-R regulated lipoprotein [TAGA]) in the pathogenesis of the emerging human pathogen Aeromonas hydrophila

Aeromonas hydrophila, a gram-negative bacterium that causes gastroenteritis, wound infections, septicemia, and other diseases in humans, produces many different virulence factors. A clinical isolate SSU of A. hydrophila possesses a cytotoxic enterotoxin Act, a potent virulence factor that is secreted into the environment through the bacterium’s type 2 secretion system (T2SS) and possesses several biological activities, including cytotoxicity, enterotoxicity, and lethality in a mouse model. The purpose of this study was to identify new virulence factors that contribute to the pathogenesis of this bacterium. We identified and characterized a type 3 secretion system (T3SS) in A. hydrophila SSU. By marker-exchange mutagenesis of the aopB gene, a crucial gene involved in the formation of the translocon apparatus, the functionality of the T3SS was elucidated, both in in vitro and in vivo models. Further, the characterization of the regulatory gene DNA adenine methyltransferase (Dam) from SSU and its role in modulating the function of both the T3SS and Act was investigated. The role of the T3SS in influencing the phenomenon of quorum sensing (QS) in A. hydrophila SSU was also conducted. This study highlights a unique link between the T3SS and Act of A. hydrophila and the production of QS molecules or lactones. While searching for potential effector proteins secreted through the T3SS of A. hydrophila SSU, the identification of a new virulence factor, ToxR regulated lipoprotein (TagA), was revealed. TagA is a zinc metalloprotease which has only been identified in the gram-negative pathogens, Escherichia coli O157:H7 and Vibrio cholerae. In A. hydrophila, TagA has been shown to play a role in the inhibition of complement by binding to and cleaving the serpin C1-INH. By recruiting C1-INH to the surface of the bacteria and cleaving it, TagA is able to significantly prevent the activation of complement at the cell surface, ultimately increasing the serum resistance of the pathogen. TagA can also target C1-INH to erythrocyte surfaces and decrease the lysis that occurs in the presence of serum. Confocal fluorescence microscopy revealed that the serpin C1-INH binds to TagA on the surface of the bacteria.

Name thesis:degree_name

PhD

Level thesis:degree_level

Doctoral

Grantor

The University of Texas Medical Branch

Year dc:date.issued

2006

Author dc:creator

• Lakshmi Pillai

Advisor dc:contributor.advisor

• Dr. Ashok K. Chopra, Ph.D. C.Sc.

Committee members dc:contributor.committeemember

• Dr. Vladimir Motin, Ph.D.
• Dr. Golda A.K. Leonard, Ph.D.
• Dr. Eric M. Smith, Ph.D.
• Dr. Chandrasekha Yallampalli, Ph.D.
• Dr. Amy Horneman, Ph.D., SM(ASCP)

• type III secretion system (T3SS)
• ToxR regulated lipoprotein (TagA)
• serum resistance
• regulation
• quorum sensing
• mouse model lethality
• DNA adenine methyltransferase (Dam)
• cytotoxicity
• complment inhibitor (C1-INH)
• Aeromonas hydrophila SSU

Statement dc:rights

• Copyright © is held by the author. Presentation of this material on the TDL web site by The University of Texas Medical Branch at Galveston was made possible under a limited license grant from the author who has retained all copyrights in the works.

Language dc:language.iso

eng

Dc Identifier Other

etd-08142006-144401

OAI identifier oai:identifier

oai:utmb-ir.tdl.org:2152.3/207