Oral immunization against experimental salmonellosis I. Development of temperature-sensitive mutant vaccines.

Mutant strains of Salmonella enteritidis were selected for their inability to proliferate at 37 C; when exposed to this temperature, these organisms formed tangled masses of long filaments in liquid media, presumably as a result of their inability to form cross septa. The mutants were also incapable of synthesizing flagella protein. A study of the biological charateristics of the mutants indicated that in most respects they resembled the parent strain of S. enteritidis; however, they were avirulent for mice, presumably because of the restriction of growth imposed by the body temperature of the animal. Preliminary studies have suggested that these mutants are highly effective in inducing protection against severe challenge infections of S. enteritidis; of especial interest is the fact that, when given orally, the mutants conferred a substantial degree of protection against oral infection with the virulent strain.