A collection of Erysipelothrix rhusiopathiae swine, fish, and cetacean strains representing nearly all 16 serotypes was analyzed for possession of the surface protective antigen (spa) family of genes and their expression products. Polymerase chain reaction (PCR) assays utilizing primers specific for spaA, spaB and spaC revealed that spa-type is not absolutely associated with serotype when two strains of serotypes previously reported to possess spaB produced amplicons with spaA-specific primers. These results were supported when a monoclonal antibody, specific for the protective domain of SpaA, reacted strongly in Western blotting with a 65 kilodalton (kDa) protein from both strains. Vaccination challenge studies were conducted in mice to evaluate an E. rhusiopathiae bacterin composed of a serotype 2 SpaA-type swine strain in its ability to protect mice against challenge with virulent fish and cetacean strains of various spa-types. Vaccinated mice were completely protected against challenge strains possessing spaA but variably protected against challenge strains possessing heterologous spa or more than one spa-type.