| Strains of Clostridium welchii were isolated from diarrhea rabbits that came from rabbit breeding farms of Laiwu, Taian and Weifang city. These field strains were identified as Clostridium welchii type A by bacteriological method and serological typing. The toxin produced by field strain and the standard strain were inactivated and mixed with 5%A1(OH)3. After concentrating, the toxoid vaccine of Clostridium welchii was successfully produced. The serum antibody's growth and decline regulation of the rabbits was also detected, which was immunized with the toxoid vaccine of Clostridium welchii type A. Furthermore, the purification method of a-toxin and the preparation method of the antitoxic serum were studied. The results indicated that the toxoid vaccine had good immunological protection effect. The a-toxin could be successfully purified by chromatographing through the SephadexG-25 and SephadexG-200. The antitoxic serum has also high antibody levels and good security.This research consists of four parts.Part I : The isolation and identification of Clostridium welchii type A. Livers, intestines of the diarrhea rabbits were collected for the isolation of the Clostridium welchii. The isolated disease bacterials were identificated as Clostridium welchii type A by bacteriological research and serological classification.PartII:The purification and identification of the a -toxin of Clostridium welchii type A. The exotoxin which produced by the Clostridium welchii was salted out two times by 50% and 40% ( NH^SO^ then the crude toxin was treated with Sephadex G-25 and SephadexG-200.The chromatography liquid which had toxin activity was gathered and concentrated .By this way , the purified a -toxin of Clostridium welchii was gained. Its SDS-PAGE figure only has one belt and its molecular weight was about 43.6KD which conformed to the standard a -toxin 's molecular weight.Partlir.The preparation of the toxoid vaccine of Clostridium welchii type A. The standard strain and the isolated strain of Clostridium welchii type A were inoculated to the nutrient broth and cultured in 40 癈 anaerobic environment, then some culture liquid was transformed into the Gordon broth, shaking cultured for 6-7 hour in 43'C anaerobic environment. The cultured liquid was centigraded with high speed and low temperature, and then they were filtered in order to remove the bacterium bodies . We got the Clostridium welchii exotoxin. The LD5o for the little white mouse was 1021 per ml (standard strain) and 10183 per ml(FD strain). At different time(8h,16h,32h,64h, 128h), the toxin was inactivated with formaldehyde. After inactivation, 5% A1(OH)3 was put in the toxoid in certain proportion, then we got the Clostridium welchii type A toxoid vaccine. The vaccine was checked for its security, immune dose. The regulation of the antitoxin's growth and decline in the rabbit's serum that immunized with this toxoid vaccine was measured. The results showed that this vaccine was very safe and had high immunity effect. From 7th day, we began to detect the antitoxin in the serum and it reached the highest titer in 30 days after immunization. In the 23rd week, the even antitoxin titer was also exceeding 3.41og2. The antitoxin's level of the serum can sustain for about 3 monthsin a high level. By the t-test, there was no remarkable difference between the even antitoxin's levels of two group rabbits that immunized with the Clostridium welchii toxoid vaccine .PaftIV:The preparation of antitoxic serum of Clostridium welchii type A. The bacterial vaccine and exotoxin of Clostridium welchii were made from the standard Clostridium welchii type A, as the first and the second antigen to immunize sheep. The sheep was vaccinated with 5, 8, 10ml of the inactivated bacterial vaccine respectively, interval-Vdays, for basic immunity, and then vaccinated with 2, 5, 10, 15, 20, 30 and 40ml of the exotoxoin respectively, also interval-7days. Seven days after the last immunity, the blood of the experimental animal-sheep was drawn and the antitoxic serum was isolate...
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