Evaluation of a whole cell, p57(-) vaccine against Renibacterium salmoninarum

A whole cell Renibacterium salmoninarum vaccine was developed using 37 degr ees C heat treated cells that were subsequently formalin fixed; this treatm ent reduced bacterial hydrophobicity and cell associated p57. Coho salmon O ncorhynchus kisutch were immunized with the p57(-) vaccine by either a comb ination of intraperitoneal (ip) and intramuscular (im) injections or per os . rn the first ex periment, ip/im vaccination of coho salmon with p57(-) ce lls in Freund's Incomplete Adjuvant (FIA) conferred a statistically signifi cant increase in mean time to death after the salmon were ip challenged wit h 4.1 x 10(6) colony forming units (cfu) of R, salmoninarum. There was no s ignificant difference in response between fish immunized with R. salmoninar um cell surface extract in FIA and those immunized with extracellular prote in (ECP) concentrated from culture supernatant in FIA. The ip challenge dos e resulted in complete mortality of all fish by Day 43. In a second experim ent, fish were orally vaccinated with p57(-) R, salmoninarum cells encased in a pH protected, enteric-coated antigen microsphere (ECAM). Fish were bat h challenged with 4.2 x 10(6) cfu ml(-1) on Day 0 and sampled at time point s of 0 (pre-challenge), 50, 90, or 150 d immersion challenge. Vaccine effic acy was determined by monitoring the elaboration of p57 in the kidneys of v accinated and control fish. Fish vaccinated orally demonstrated a significa ntly lower concentration of p57 (p < 0.01) at Day 150 post challenge compar ed to fish receiving ECAMs alone. Fish receiving p57(-) cells without ECAM coating also showed a significantly lower p57 level (p < 0.03) versus contr ol. In contrast, fish injected intraperitoneally with the p57(-) cells or f ish fed p57(+) R, salmoninarum cells in ECAMs demonstrated no significant d ifference (p > 0.05) versus controls. In summary, these studies suggest the preliminary efficacy of 37 degrees C treatment of R, salmoninarum cells as an oral bacterial kidney disease vaccine.