A Physical, Cultural, and Nutritional Study of "Leptospira Interrogans" Serotype "Hardjo" with Emphasis on Antigenicity, Immunogenicity, and Viability

Abstract

The problem. "Leptospira interrogans" serotype "hardjo" has been indicated as the cause of abortion and clinical leptospirosis in cattle. It is a fastidious organism and has been difficult to reisolate from infected animals. This study was designed to determine if the nutritional requirements were different from other leptospires and if an optimum incubation temperature could be established. Secondly, studies were done to see what effects these parameters had on antigenicity and imunogenicity. Procedure. Cells of an avirulent laboratory adapted strain of "L. hardjo" were grown in different formulations of bovine albumin polysorbate media (BA-P80). Single and multiple deletions and different sources of ingredients for the medium were evaluated. Continuous growth was measured over a predetermined range of temperatures. The antigenicity of cells incubated at two temperatures were compared in a microscopic agglutination test. The efficacy of two heat-inactivated bacterins was evaluated by challenge of vaccinated hamsters with a kidney infective isolate. Findings. The avirulent strain grew best at temperatures between 29 degrees and 31.5 degrees C. Optimum growth occurred in the complete BA-P80 media formulation. No difference was seen in the antigenicity of either 29 degree or 37 degree C. incubated leptospires. The bacterin prepared with whole cells grown at 37 degrees C was more efficacious than the bacterin using cells grown at 29 degrees C. Conclusions. The nutritional requirements for "L. hardjo" did not differ from many of the other leptospires that have been studied. Bovine albumin polysorbate 80 media was best suited for routine propagation of antigens and isolation of leptospires from infected tissues. Heat-inactivated whole cell bacterins provided excellent protection. Recommendations. Attempts should be made to duplicate the nutritional studies and growth temperature studies using several virulent "L. hardjo" isolates. Further research needs to be done to determine why a whole cell bacterin prepared using antigen incubated at 37 degrees C provided greater immunity.