Erysipelothrix rhusiopathiae is a ubiquitous gram-positive rod. It is able to cause disease in a wide range of animals. In humans the organism is known to cause erysipeloid and endocarditis. Although Erysipelothrix rhusiopathiae has never been known to cause disease in fish, it can persist for long periods of time in their external mucus. Consequently, this organism presents an occupational risk to fishermen as well as to those who handle fish because of the opportunities to acquire the organism through small cuts on the hands and arms. In marine mammals, however, Erysipelothrix rhusiopathiae is often the cause of a fatal form of septicemia.

In this study, six recent isolates from the Shedd aquarium, isolates from Sea World of Texas and Sea World of California, as well as several other previously acquired environmental isolates from various marine mammal institutions, were compared to several ATCC reference isolates of Erysipelothrbc rhusiopathiae and Erysipelothrix tonsillarum using various immunological, microbiological and molecular biology techniques. All isolates and reference strains were tested for their ability to ferment twelve different carbohydrates and for their ability to produce caseinase, DNAase, amylase, tryptophanase and urease. In addition, miscellaneous tests including nitrate reduction and citrate utilization were performed. Extracted surface proteins from all of the isolates and reference strains were western blotted and immunostained with antisera preparations raised against extracted surface proteins or against heat-killed bacterial suspensions representing several Erysipelothrix rhusiopathiae serotypes. Additionally, all of the environmental isolates and ATCC reference strains were analyzed by the polymerase chain reaction using species specific primers that amplify base pair products that are specific for Erysipelothrix rhusiopathiae, and Erysipelothrix tonsillarum. Furthermore, all of the isolates were analyzed for the presence of plasmids. Microbiological and immunological testing revealed some differences among the isolates and between the isolates and the reference strains. All of the environmental isolates were confirmed as Erysipelothrix rhusiopathiae, however, the polymerase chain reaction proved to be more discriminatory in its ability to distinguish between Erysipelothrix rhusiopathiae and Erysipelothrix tonsillarum.