EVALUATION OF SEROLOGICAL AND CULTURAL METHODS FOR THE DIAGNOSIS OF CHRONIC SALMONELLOSIS IN MICE

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Abstract
Mice were infected by inoculation of varying doses of a virulent culture of Salmonella typhimurium directly into the stomach. Feces were cultured at intervals on Brilliant Green and Eosin Methylene Blue Agar. Most survivors shed organisms consistently during the early stage of infection, but, after 1 month, a large number had become intermittent shedders. These animals would have been considered salmonella-free if cultured at a time when they were not shedding the organism. Serological tests to detect antibodies in their sera, therefore, were investigated. Standard agglutination, and hemagglutination and hemolytic tests with the use of sheep erythrocytes modified with extracts of S. typhimurium, were performed with sera from infected mice. It was possible to detect smaller amounts of antibody in the sera by means of the hemolytic test, and this test was often positive when the others were negative. Antibodies detectable by the hemolytic test appeared within 21 days after inoculation, and were present in the sera of surviving animals for 3 months or longer. All animals known to be infected gave positive serological reactions. Cultural techniques were most satisfactory for detection of salmonellosis during early stages of infection, and serological tests were or primary value at later intervals. Concurrent use of both techniques ensured discovery of the largest number of infected animals.