TWENTY-SECOND ANNUAL EASTERN FISH HEALTH WORKSHOP ROYAL PAVILLION RESORT, ATLANTIC BEACH, NC MARCH 18 - 20, 1997 An Atenuated Isolated of Edwardsiella ictaluri: Identification of a virulence factor? Richard K. Cooper1 and Emmett B. Shotts2, Jr. 11Department of Veterinary Science, Louisiana Agricultural Center, Louisiana Agricultural Experiment Station, Baton Rouge, LA 70803;2Department of Medical Microbiology, College of Veterinary Medicine, University of Georgia, Athens, GA 30602 Edwardsiella ictaluri, cause of enteric septicema (ESC) of channel catfish (Ictalurus punctatus)is the major cause of disease in commercial catfish culture. The bacterium has been characterized for survival in the environment, modes of entry into channel catfish, host range, and phenotypic and biochemical analysis. Yet, little is known about virulence factors associated with E. ictaluri, i.e.- how the organism enters the host and survives its immune system. By transposon mutagenesis (transposon derivative 103, kan1), we targeted a suspected virulence gene chondroitinase, which gives the bacterium the ability to degrade chondroitin sulfate. After delivery of the transposon to E. ictaluri (Georgia isolate 6022), bacteria was selected by resistance to kanamycin, and then for lack of activity on chondroitin sulfate media. Chondroitin negative isolates were screened phenotypically for loss of other biochemical properties, and based on these results, isolate MEI15 was chosen for further study. The isolate was evaluated for loss of virulence in channel catfish by immersion and injection. Neither challenge method caused mortality in channel catfish, whereas the virulent parent strain killed >90% of the control fish. Isolation of the mutant MEI15 and passage through catfish failed to restore virulence. We have identified the gene in the wildtype and MEI15 by the polymerase chain reaction and are sequencing and cloning gene. Information at the genomic level and the challenge data obtained from channel catfish may begin to provide information on the role of chondroitinase in the virulence of E. ictaluri and help to formulate a vaccine that protects channel catfish against ESC. Return to 22nd Annual Eastern Fish Health Workshop Return to Leetown Science Center Home Page