Evaluation Of A Siderophore Deficient And An AroA Live Attenuated Vaccine For Protection Against Photobacterium damselae Subsp. piscicida In Hybrid Striped Bass     Ron A. Miller1, John P. Hawke1, and Ron L. Thune1, 2   1Louisiana State University, Department of Pathobiological Sciences, School of Veterinary Medicine; 2Louisiana State University, Department of Veterinary Science, School of Veterinary Medicine                 Photobacterium damselae subsp. piscicida (Ph. damselae) is a Gram negative, facultative intracellular pathogen that is the causative agent of Photobacteriosis.  This highly pathogenic organism is the source of significant losses in farm raised fish populations in the U.S., Japan, and the Mediterranean region. To evaluate the efficacy of two live attenuated Ph. damselae mutants, and a wild-type (strain LA91-197) formalin-killed preparation as potential vaccines, an infection trial was completed using hybrid striped bass (HSB) as the model.  Using lethal dose-50 trial data obtained from both immersion and injection studies, a safe vaccination dose was targeted for each of the live attenuated mutants.  These vaccines should be capable of invading, persisting, eliciting a protective immune response, and being cleared.  In addition to looking at the degree of protection provided by the vaccines after a challenge with the wild-type, specific antibody levels to Ph. damselae were measured individually over the course of the 6 week trial by an indirect enzyme-linked immunosorbent assay (ELISA). HSB immunoglobulin was semi-purified from whole serum using an inexpensive simple dialysis purification method.  Previous attempts to generate immunodiagnostic reagents to the HSB Ig have resulted in a high degree of cross-reactivity between the antibody to the fish Ig, and to the bacterial whole cell lysate bound to the ELISA plate.  In an attempt to circumvent this cross-reactivity, polyclonal rabbit antisera was generated against HSB immunoglobulin that was deglycosylated using mild periodate oxidation.  To date, no study has attempted to correlate protection with elevated levels of specific hybrid striped bass (HSB) antibody to Ph. damselae after vaccination and subsequent challenge. In this study there was no correlation between specific antibody levels and relative percent survival.  In addition, the live attenuated vaccines yielded 100% protection by immersion and 18.3% and 76.3% by injection, and the wild-type killed vaccine surprisingly only yielded an 8.0% relative percent survival.