TWENTY-FIFTH ANNUAL EASTERN FISH HEALTH WORKSHOP MARCH 10-13, 2000   Characterization Of Photobacterium damselae Subsp. piscicida From Hybrid Striped Bass Cultured In Louisiana     John P. Hawke 1, R.L. Thune 1,2 and R.K. Cooper 1,2   Department of Veterinary Microbiology and Parasitology1 And Department of Veterinary Science2; Louisiana State University, School of Veterinary Medicine, Baton Rouge, LA 70803     Photobacterium damselae subsp. piscicida, formerly “Pasteurella piscicida”, is an important pathogen of hybrid striped bass cultured in brackish water. Photobacteriosis has been diagnosed yearly, since 1990, as the cause of extensive mortality on fish farms in coastal Louisiana. Five strains of the bacterium from the Louisiana Gulf Coast were characterized according to their biochemical phenotype, enzyme activities, plasmid profile, antimicrobial susceptibility, G+C ratio and antigenic cross reactivity. Gulf Coast isolates were compared with representative isolates from Chesapeake Bay USA, Greece, Japan and Israel.  Gulf Coast strains of P. damselae subsp. piscicida were found to be almost identical with strains from other geographic locations in biochemical phenotype, enzyme activity, and antigenic cross reactivity. Differences among the isolates were noted in plasmid profile and antimicrobial susceptibility. Louisiana isolates were found to possess identical plasmid banding patterns with the exception of strain 90-744 which was missing one of the common bands. Louisiana isolates were unique when compared to strains from other geographic locations typically possessing two large plasmid bands in the 30-40 kb range and two smaller bands of 8.0 and 5.0 kb in size. Isolates from Israel, Greece and the isolate from Chesapeake Bay (ATCC 17911) exhibited banding patterns that were similar to each other but different from Louisiana isolates. Japanese isolates also produced unique patterns that were different from all others tested. Differences were seen in susceptibility to chloramphenicol, Romet, oxytetracycline, erythromycin, and kanamycin.  Resistance to Romet and oxytetracycline by some Louisiana strains was the apparent result of administration of medicated feeds and the subsequent acquisition of an R-plasmid. Japanese strain EP94-001 was resistant to chloramphenicol, oxytetracycline, erythromycin and kanamycin. All other strains tested were uniformly susceptible to the antibiotics tested.         Return to 25th Annual Eastern Fish Health Workshop Return to Leetown Science Center Home Page