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

Abstract

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. [Projekat Ministarstva nauke Republike Srbije, br. 31085 i br. 31088]

Keywords

• Listeria monocytogenes
• vaccine
• saponin
• sheep