Immunizing mice using different combination antigens of the PI-2a fimbria subunit of Streptococcus agalactiae

Document Type: Full paper (Original article)


1 Key Laboratory of Preventive Veterinary Medicine and Animal Biotechnology, Shandong Binzhou Animal Science and Veterinary Medicine Academy, Binzhou, 256600, China

2 Inner Mongolia Autonomous Region Engineering Technology Research Center of Prevention and Control the Pathogenic Bacteria in Milk, Tongliao 028043, China

3 Shandong Lvdu Bio-Sciences and Technology Co., Ltd., Binzhou, 256600, China


Background: Streptococcus agalactiae is the main causal pathogen of bovine mastitis (BM), causing considerable economic loss to the dairy industry worldwide. Vaccines against S. agalactiae play an important role in preventing disease. Aims: The aim of this study was to evaluate the immunoprotection of S. agalactiae pilus island fusion proteins, ancillary protein 1-ancillary protein 2 (AP1-AP2), ancillary protein 1-bone protein (AP1-BP), bone protein-ancillary protein 2 (BP-AP2), and ancillary protein 1-bone protein-ancillary protein 2 (AP1-BP-AP2) in Balb/c mice. Methods: Four kinds of fusion antigens and the same volume of Freund’s complete adjuvant were mixed vigorously to prepare fusion antigen immuno-samples. The mice were immunized 4 times (on the 0th, 7th, 14th, and 28th days) with these samples with an immunizing dose of 50 mg/mouse. After the 4th immunization, serology tests were used to evaluate the antibody. The antibody titre produced by AP1-BP-AP2 fusion antigen was the highest, at up to 1:25600. The mice were then injected with 0.5 ml of 2 × 104 CFU/ml clinically isolated S. agalactiae at day 50 and observed daily for the following 7 days. Results: Statistical analyses showed that these 4 kinds of fusion antigens had good protective immunity. Among them, AP1-BP-AP2 fusion antigen had the best protective immunity in Balb/c mice, with an immune protection index (PI) of 80%. Conclusion: This research provides a reliable theoretical basis for screening candidate antigens of the subunit vaccine and detecting antigen preparations of S. agalactiae.


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