Volume 62 (2012) Issue: 2012 No#5-6

A study on the inactivated bivalent vaccine prepared from serotypes 1/2a and 4b Listeria monocytogenes for the control of listeriosis in sheep

Author(s): Bacić D, Obrenović Sonja, Dimitrijević B, Jonić B, Žutić Jadranka, Ašanin N

Keywords:Listeria monocytogenes, vaccine, saponin, sheep

In this study, the protective effects of two bivalent inactivated vaccines were evaluated. Vaccines were prepared from Listeria monocytogenes, serotypes 1/2a and 4b, as the most frequent in our and surrounding epidemiological areas. Vaccine A consists of whole L. monocytogenes bacteria cells, inactivated with 0.4% formaldehyde and aluminium hydroxide as a carrier. Vaccine B contains 0.1% saponin in addition to ingredients of vaccine A. Evaluations of these vaccines were performed in 60 sheep, divided into four groups (n=10) with a corresponding negative control group (n=5). After 14 days, boosterisation of all animals was performed. In order to evaluate the immune response, blood samples were obtained every 14 days during the next 6 months. Antibody titres were determined by microaglutitation (MAT) and complement fixation tests (CFT). Comparative analyses of antibody titres, induced by vaccines A and B, show that the latter (with saponine) significantly increased the level of antibody titres (p<0.01). The levels of immune response were also significantly impacted by the total number of bacteria and vaccine dosage (p<0.01). The bivalent vaccine containing 0.1% saponin (vaccine B) in 5.0 mLx 106 cfu/mL (colony-forming units per milliliter) dosage shows a protective effect after challenge with L. monocytogenes. The protective levels of this antibody were 1/80 and 1/16, determined by MAT and CFT, respectively. Antibody titres were significantly higher after boosterisation (p<0.01) and protective levels could be detected in the sera of vaccinated animals during the next 6 months. Therefore, it is strongly recommended to perform boosterisation two weeks after the initial vaccination.