Listeria monocytogenes-vaccine: production and control

The experiments described in this paper were designed in order to develop the basis for the production and potency testing of a live vaccine against listeriosis. The vaccine contains the serovars 1/2 a and 4b of Listeria monocytogenes (L. m.). a) Production. R-forms of both serovars with attenuated mice virulence were used as antigens. The vaccine strains can be kept stable by means of lyophilisation. The vaccine should contain at least 1 X 10(8) living bacteria of each serovar. During production, a cultivation temperature of + 22 degrees C is employed in order to guarantee the formation of somatic (O-) and flagellar (H-)antigens. b) Potency testing. The quantitative mice protection test is the only suitable method for potency testing: subcutaneous vaccination, followed ten days later by challenge with graded doses of sufficiently mice pathogenic, homologous forms of both serovars of L. m. The protection index calculating according to Kärber should be at least 100. Due to the possible decline of the number of living bacteria during storage which could result in decreased potency of the vaccine, the expiration date of the vaccine should be one year after production. It was found that the antibody titres of vaccinated animals are without any value for estimating the protective potency of vaccines.