Investigations of protective effects of bivalent inactivated vaccine prepared from serotypes 1/2a and 4b Listeria monocytogenes on mice

The objective of these investigations was to check on laboratory white mice the protective effect of an inactivated bivalent vaccine prepared from serotypes 1/2a and 4b L. monocytogenes. Following verification of the sterility and toxicity of the prepared vaccine, the mice were divided into 6 groups with 10 animals in each group. The first and second group of mice were administered the vaccine without saponin (vaccine A) and the third and fourth group the vaccine with saponin (vaccine B). Mice of the fifth and the sixth group were not vaccinated and served as a negative control. Two weeks following vaccination, the experimental groups were revaccinated, with the exception of the two control groups. Two weeks following revaccination, all groups were artificially infected with serotypes 1/2a and 4b L. monocytogenes. During the course of the investigations (60 days) a total of 4 mice died in the vaccinated groups. Mice of the control groups started dying after day 7, and the last mouse in these groups died 14 days after the infection. Examinations of preparations of parenchymatous organs of the dead mice stained according to Gram proved the presence of L. monocytogenes. Homogenates of parenchymatous organs were sown on tryptose agar for reisolation and a pure culture of L. monocytogenes was obtained. Through the use of specific antiserums, serotypes 1/2a and 4b were confirmed. Considering the total number of vaccinated mice in the experiment and the percent deaths (10%), it can be said that the investigated vaccine with saponin had a satisfactory protective effect. [Projekat Ministarstva nauke Republike Srbije, br. TR-20142 i TR-31088]