Construction and comparative study of immunogenicity of bp26 deletion mutant of Brucella vaccine strain M5-90 / 中国地方病学杂志

ABSTRACT

Objective To construct the bp26 deletion mutant of Brucella vaccine strain M5-90 (M5-90Δbp26),to compare its immunogenicity with parental strain(M5-90),and to develope a new candidate vaccine strain of Brucella melitensis with reduced virulence that can be used to distinguish vaccinated livestock from infected animals.Methods Mutant vaccine strain of Brucella melitensis was constructed by conventional molecular biology techniques then the genetic stability of mutant M5-90Δbp26 was tested and its conventional bacteriological nature was identified; 1.0 × 109 CFU/2 ml doses of M5-90Δbp26 strain and the parental strain were used to vaccinate 3 sheep; sera were analyzed for reactivity against BP26 by Western blotting and for agglutination activity; to analyze the virulence of mutant and parental strain,mice were injected with 1.0 × 106,6.0 × 106 and 2.0 × 107 CFU/0.2 ml doses of M5-90 and M5-90Δbp26,respectively,and clinical symptoms were monitored and the death of mice was recorded.Results The M5-90Δbp26 was successfully generated and reversion was not observed in 15 generations.The size of PCR products was 629 bp while the parental strain was 1279 bp.The sequence analysis showed a 650 bp missing in M5-90Δbp26.The conventional bacteria identification tests confirmed that the mutant was depth variant strain,including mono-specific antiserum M type transformed into R,and the BK2 phage based splitting assay converted from the positive to the negative.Western blotting showed the purified BP26 protein was recognized by the serum against the parental strain while not by the serum against M5-90Δbp26 strain.Agglutination test showed the level of the serum antibody induced by M5-90Δbp26 strain(150) was significantly lower than that of serum induced by parental strain(＞ 1800).Virulence test showed that M5-90Δbp26 strain was less virulent than parental strain.Conclusions M5-90Δbp26 has been successfully constructed.M5-90Δbp26 of Brucella melitensis has the characteristic of reduced virulence and has a potential as brucellosis candidate vaccine strain permitting serological discrimination between diseased and vaccinated livestock.