Produção e avaliação antigênica de bacterina contra Streptococcus agalactiae

Abstract

Bovine mastitis is an inflammatory process of the mammary gland due to the interaction of animals related to the animal, pathogen and environment. This disease is generally caused by microbial invasion of the mammary gland, mainly by bacteria. Among the main pathogens involved in its aetiology, Streptococcus agalactiae stands out, which determines the high clinical levels of new infections, leading to a decrease in the quantity and quality of milk produced by the infected animal or herd. Among the measures of control and prevention for bovine mastitis the use of vaccines has been extensively, aiming to reduce de level of new infections and duration and severity of cases. Therefore, the objective of this work was to develop and evaluate the antigenicity of one bacterin for the control and prevention of bovine mastitis caused by S. agalactiae. To this propose, it was produced an experimental bacterin adjuvanted with aluminum hydroxide, containing the strains SA522 and SA199 at the concentration of 1x109 UFC / mL of each isolate. For antigenicity tests of vaccine, 45 pregnant cows belonging to a dairy farm located in the south of Minas Gerais, which were negative for S. agalactiae were used, as 30 in vaccinated group and 15 in control group. Animals of vaccinated group received two doses of bacterin (5mL/dosis) by the subcutaneous route with interval of 21 days. The control was inoculated with placebo (5 mL sterile saline). Previously to vaccination was performed blood and milk collecting blood from each animal in order to assegurate that they were not infected by S. agalactiae. Nine days after second vaccinal dosis (D30) blood collections of all animals of vacinal group and control groups were performed and dosages of anti-S. agalactiae immunoglobulins were done by indirect enzyme-linked immunosorbent assays (ELISA). Due to the lack of ELISA kits for anti -S. agalactiae antibodies in cattle, an ELISA standardization was performed for this purpose. In addition, blood serum samples from uninfected cows and cows naturally infected by S. agalactiae were subjected to the ELISA for the detection of IgG. Data were statistically analised by Software R and GraphPad Prism Software, with a 5% statistical error level. Statistically significant differences (p <0.05) for test T, were observed for the vaccinated group before vaccination (D0) and after a second vaccine dose (D30) (p = 0.0056). The animals of the control group didn´t show differences in antibodies levels in D0 relation D30 (p = 0.3303). The developed bacterin was able to induce the production of anti-S agalactiae antibodies in vaccinated cows and the standardized ELISA test proved to be effective in the detection of serum antibodies in these animals. It was not possible to detect serum antibodies against S. agalactiae in the naturally infected animals, suggesting the absence of their production in natural infections of cattle caused by this pathogen. Future studies should be conducted to evaluate the immunogenicity of this vaccine in S. agalactiae-infected herds.