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INVESTIGATOR: Rogge, M. L.

PERFORMING INSTITUTION:
LOUISIANA STATE UNIVERSITY
202 HIMES HALL
BATON ROUGE, LOUISIANA 70803-0100

THE ROLE OF TYPE VI SECRETION IN EDWARDSIELLA ICTALURI VIRULENCE

NON-TECHNICAL SUMMARY: The gram-negative pathogen Edwardsiella ictaluri is the etiological agent of enteric septicemia of catfish (ESC), an economically-important disease of channel catfish (Ictalurus punctatus). Channel catfish and trout are the major aquaculture species of the United States, with catfish farming accounting for approximately 90% of the total finfish aquaculture production in the United States in 2009. Enteric septicemia of catfish is reported in all catfish production regions of the US, and losses due to ESC were reported on over 60% of production facilities. Recent research has identified the importance of bacterial secretion systems in E. ictaluri virulence. Edwardsiella ictaluri encodes a complete type VI secretion system (T6SS), which are recently identified bacterial secretion systems commonly associated with pathogenic organisms. Relatively little is known about how T6SS are involved in bacterial pathogenesis, but preliminary data indicates that the E. ictaluri T6SS is required for virulence. Further understanding of the role of the T6SS in E. ictaluri pathogenesis will provide information about the host-pathogen interaction, leading to improved knowledge of pathogenesis, as well as provide information for vaccine development.

OBJECTIVES: The goal is to determine the role of the E. ictaluri type VI secretion system (T6SS) in virulence associated with enteric septicemia of catfish (ESC). Based on preliminary data, the T6SS is an important virulence factor of E. ictaluri. Further understanding of how this system is involved in pathogenesis will lead to effective treatments against this deadly fish pathogen. Furthermore, this information will be useful to advance the understanding of the role of the T6SS in pathogens of higher vertebrates, including Salmonella, Yersinia, Burkholderia, Vibrio, and others. Using ESC to study T6SSs provides a significant advantage in that test subjects are readily available for in vivo studies, and the host/pathogen relationship represents a natural disease system and not a model. Our lab is capable of screening virulence mutants in a number of in vitro, ex vivo, and in vivo assays, including gene expression analyses by quantitative real-time PCR, western blot, phagocytic and non-phagocytic cell culture assays, and in vivo invasion, persistence, and mortality assays to evaluate virulence. This research puts forth two specific objectives that will confirm the role of the T6SS in pathogenesis of E. ictaluri, identify proteins secreted by the E. ictaluri T6SS, and identify how the T6SS is involved in pathogenesis. The first objective of this research is to identify the conditions involved in the expression of the E. ictaluri T6SS by evaluating expression of T6SS genes in varying culture conditions. Furthermore, proteins secreted by the T6SS will be identified and evaluated for their role in E. ictaluri pathogenesis. The second objective is to determine the role of the E. ictaluri T6SS in pathogenesis. The effects of T6SS secretion on intracellular replication within channel catfish cells will be evaluated, as well as effects in vivo within the channel catfish. Expected outputs from this research include the results of the studies being presented at national and international meetings in addition to peer-reviewed publications.