Identification Of Factors Involved In The Pathogenesis Of Edwardsiella ictaluri     Ronald L. Thune1, 2, Denise H. Fernandez1, Jennifer L. Benoit1, and Maria Kelly-Smith1   1Dept. of Veterinary Science, LSU Agricultural Center, 2Dept. Pathobiological Sciences, LSU School of Vet. Med., Baton Rouge, LA     Enteric septicemia of catfish (ESC) is recognized as the most serious disease facing the commercial channel catfish industry.  While much is known about the pathology of Edwardsiella ictaluri, the causative agent of ESC, little is known about the virulence factors associated with infection.  In an attempt to identify virulence genes of E. ictaluri, mutants were created by signature tagged mutagenesis (STM), an in vivo system that allows for the identification of bacteria unable to grow in the host due to defects in genes affecting invasion and survival.  To date, 133 different mutant pools containing a total of 1197 individual mutants have been screened and 37 mutants were identified that did not survive in the catfish host. Cloning and sequencing thus far has identified several nutritional genes, including a gene encoding N-acetylglucosamine-6-phosphate deacetylase, a gene that may be involved in the synthesis of folate, the miaA gene, encoding tRNA delta2-isopentylpyrophosphate transferase, the guaB gene, involved in the biosynthesis of guanine, and the glucose inhibited division protein.  Possible virulence genes based on BLASTX searches include a putative 0-antigen transporter gene, insA, which is involved in Shiga toxin regulation, pilL, an essential gene in Type IV pilin formation in Salmonella enterica, several genes involved in type III secretory systems, and several genes having no matches to the National Center for Biotechnology Information databases.