Abstract
Two types of Escherichia coli, C1 and C2, used in the making of a vaccine against bovine colibacillosis in Madagascar, are studied. Bacteria were counted by the Malassez cell. The LD100 of the two strains are respectively 1.09×108 and 1.66×107 bacteria/ml. They were inactivated by 5‰ formalin to produce the respective antigens at a titer of 2×109 bacteria/ml. The antigens thus obtained are added with adjuvant based on potassium alum to obtain vaccine prototypes P1 and P2. Each vaccine prototype was injected subcutaneously into batches of mice followed by a booster after 15 days of the first dose. The batches of vaccinated mice are tested after 15 days of the booster dose and each receive the LD100 of the strain. During the 10 days observation time, mice vaccinated with P1 are protected against C1 and those receiving P2 are protected against C2. On the other hand, P1 does not protect mice against C2 and P2 does not protect them against C1. The duration of protection is 12 months. The 2 prototypes maintain their effectiveness for 6 months of storage at 4°C.
Keywords: Escherichia coli, vaccine, bovine colibacillosis