Protective activity of different immunosera against Clostridium chauvoei

The protective activity of several antiserum preparations against C. chauvoei strain 5078 challenge is studied. Immunosera were obtained from the following antigenic preparations from 12 h-old cultures of C. chauvoei at 37 degrees C in anaerobic conditions: (1) flagellar suspension (F); (2) cellular extract (CE): lyophilised cells (0.5 g) extracted by using veronal buffer, pH = 8.6; (3) formaldehyde-treated cell suspension with 0.5% of formol (FC); and (4) heated cells boiled for 2 h(ØC). Lots of white rabbits were inoculated by i.v. route for each immunogenic preparation. The immunosera agglutination titres were: F:1:476, CE: 1:13186; FC 1:476 and ØC: 1:64. Passive immunisation was carried out by injecting by the i.p. route groups of ten mice with 0.5 mL of pooled sera. Mice were challenged 6 h later with a spore suspension in CaCl2 2.5% containing 10 LD50. Both immunised and non-immunised animals were observed for 4 days. Anti-CE and anti-FC protected 100% of the animals, while anti-F and anti-ØC protected 75% and 50%, respectively. Results showed that protective antigens were extracted by the veronal buffer, and that heat destroys some of them. Although FC protected 100% of immunised animals, it has been shown elsewhere that CE presented the same protective response in mice when diluted at least 1:500. Results also show that flagella contributes in part to the immunogenicity of the strain.