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Identification fo Surface Proteins of Streptococcus equi With Potential in Vaccine Development
Department of Veterinary Sciences
Existing vaccines against equine strangles are either of low efficacy in the field or are associated with adverse side effects including abcessation. The recently available genomic DNA sequences of S. equi and S. zooepidemicus give access to the genes for proteins potentially expressed on the bacterial surface and which may be involved in stimulating protective immune responses in the horse.
The project will evaluate these proteins following their expression in E. coli by screening them with antibodies from immune resistant horses and then testing pools of reactive candidate proteins by vaccinating groups of experimental ponies. These ponies will then be challenged by commingling with an infected pony and their resistance to strangles evaluated.
Proteins with protective ability will be candidates for inclusion in new generation strangles vaccines that are likely to be effective and safe. These proteins will also be valuable in development of in vitro tests that correlate with protection.
2010 Project Description
Analysis of the genomic sequence of Streptococcus equi 4047 revealed 29 genes for sortase-processed (LPxTG anchor motif) surface proteins. An additional 8 genes with this characteristic were pseudogenes in S. equi but were intact coding sequences in the closely related S. zooepidemicus. % amino acid identity of the 29 LPxTG containing proteins in S. equi and zooepidemicus ranged from 39.0 to 99.5 with a mean value of 78.6.
Proteins showing lower identity percentages or which are not expressed by S. zooepidemicus are likely to have roles in the enhanced virulence of S. equi and the associated S. equi specific immune response of the horse. The proteins will therefore be studied in order of ascending % identity. Proteins SeM, SzPSe, Fne A-E, Cne, Se46.8, Se75.3, Tag (Se51.9), Se110.0, Scl C, E, F and E ag studied previously in our laboratory and elsewhere will be excluded. Cloning and expression of the remaining 11 proteins is planned using pET-15b and E. coli BL21.
Availability of the entire set of the sortase-processed surface exposed proteins of S. equi will allow a complete evaluation of the proteins singly and in combination as potential vaccine targets.
Timoney, J.F. 2010. Streptococcus. In: Pathogenesis of Bacterial Infections in Animals. 4th Edition. Eds: C.L. Gyles, J.F. Prescott, J.G. Songer and C.O. Thoen. Blackwell Publishing, pp 51-73.