Protection against bacterial infection by urea extracts from Salmonella

Immunization assays were performed in NMRI mice using urea extracts from both the S-form and an R-mutant of S. typhimurium. Our results show that, apart from providing protection against infection, both vaccines induced a DTH (delayed type hypersensitivity) reaction against the antigen extract. The strength of the DTH reaction depended on the type of test antigen used, the urea extracts proving to be superior to extracts obtained by ultrasonication. With the urea extract, all animals responded in the foot pad test. Both parameters of the immune response, protection against infection and the strength of DTH, could be further enhanced by a lipopeptide adjuvant, which was effective both in mixture and conjugate form; the humoral immune response was not enhanced. Thus, urea extract vaccines from S. typhimurium induce a cell-mediated response which can be further enhanced by lipopeptide adjuvants.