PRIMARY AND SECONDARY ANTIBODY RESPONSE TO COMPOSITE FORMALIN-INACTIVATED <i>STAPHYLOCOCCUS AUREUS</i>, <i>STREPTOCOCCUS AGALACTIAE</i> AND <i>ESCHERICHIA COLI</i> IN RABBITS

Abstract

Twenty buffaloes clinically positive for mastitis were selected for the collection of milk samples. Staphylococcus aureus, Streptococcus agalactiae and Escherichia coli were isolated from milk of mastitic buffaloes according to the procedures recommended by National Mastitis Council Inc., USA. The composite antigen containing S. aureus, Str. Agalactiae and E. coli was then prepared and the concentration of each isolate was adjusted to 1 x 10⁹ cells / ml. To evaluate the antibody response, nine adult healthy rabbits were divided randomly into three groups (A, B and C) consisting of 3 rabbits each. Composite antigen preparation was injected subcutaneously to the rabbits of groups A and B @ 0.2 ml / rabbit while each rabbit of group C inoculated with 0.2 ml normal saline and served as control. The rabbits of group B were given a booster dose at day 15 of the primary injection to see the secondary antibody response. The level of antibodies specific to S. aureus, Str. agalactiae and E. coli were assayed by indirect haemagglutination test (HA) and finally geometric mean titre (GMT) was calculated. At day 0 to 15, it was observed that the antibody titre was almost same in both groups. At day 30 significant difference in antibody titres was observed between group A and B with GMT of 9.8 against S. aureus, and Str. agalactiae in group A whereas in group B GMT was 97.0 against S. aureus and 39.4 against Str. agalactiae which was higher than group A. The GMT against E. coli was 12.1 and 24.3 in group A and B, respectively. At day 45 and 60 there was progressive decrease in antibody titre against Str. agalactiae in group B. The antibody titre against S. aureus first increased at day 45 and then decreased at day 60 whereas the antibody titre against E. coli remained persistent till day 60 in rabbits of group B. Furthermore, the primary antibody response to E. coli of composite antigen was higher (GMT, 12.1 at day 15) compared with S. aureus and Str. agalactiae (GMT, 9.8 at day 15) whereas the secondary antibody response to S. aureus was higher (GMT, 128) compared with Str. agaiactiae and E. coli (GMT, 24.3 at day 45).