Murine model for experimental studies on attenuated mutants of a Pasteurella multocida strain with pathogenicity for the calf. 2. Primary immunization against lethal infection, using fully attenuated streptomycin-dependent (Sm-d) mutant and booster immunization with partially attenuated streptomycin-dependent (Sm-id) revertants]

An experimental study was conducted into the immunisation of mice to a strain of Pasteurella multocida with pathogenicity for calf. Here are the findings: (a) The attenuation of Sm-id revertants was measured with reference to the order of extinction and compared to the wild strain. (b) A selected range of Sm-id revertants with differentiated attenuation is presented. (c) Single immunisation, using fully attenuatted Sm-d mutant does prevent lethal infection with partially attenuated Sm-id revertants, although it is ineffective against wild strain infection. (d) Immunity against 100 times the lethal dose of the wild strain can be achieved by two immunisations, that is primary antigen application, using fully attenuated Sm-d mutant, and booster immunisation, using partially attenuated Sm-id revertant.