Evaluation of three dilutions of E. coli antigen in immunogenicity in balb/c mice

Enterotoxigenic Escherichia coli (E. coli) (ETEC) is the common cause of bacterial diarrhea and mortality in calves. Due to antibiotic resistant, study on vaccination as the main prevention method is important. In current study, three dilutions of E. coli K99 antigen were evaluated for immunization of balb/C mice. Bacterial culture was inactivated by formaldehyde and washed twice by sterile PBS. Sedimentation products were adjusted in three dilutions of 3 × 107, 3× 1011 and 3× 1013 CUF/m1 due to McFarland standard tubes. Three groups each consisting of 10 mice were set as experimental groups which received two subcutaneous injections doses of different concentrations with two weeks intervals. The control groups (10) received placebo. Mice blood samples were collected during 10 weeks and antibody titer was evaluated by Elisa. Serum titers in all three experimental groups increased from 4th to 8th week and then decreased gradually. No differences were observed between groups two and three, but differences were observed between groups one and two, and one and three. Immunization by whole cell antigen was not specific but was complete. On the other hand; immunization was carried out against each antigenic epitope. When the immune cells sites are occupied by antigenic epitopes and then saturated, excessive concentration of antigen does not have much impact on the immunogenicity.