Evaluation of Immunoreactive Protiens of Streptococcus Zooepidemicus for Potential as Vaccine Components

Streptococcus zooepidemicus of Lancefield group C is an important opportunistic pathogen of the equine respiratory and reproductive tracts. A normal tonsillar and mucosal commensal, it becomes invasive under conditions of stress such as concurrent virus infection, weaning, high temperature, prolonged transportation and failure of uterine involution. Moreover, it has recently emerged as a cause of fatal hemorrhagic pneumonia of shelter dogs in the US, and also in horses on a US race track in 2008. Hemorrhagic pneumonia was apparently common in horses in urban areas of N. America in the early 1900's. Virulence factors involved and their regulation are poorly understood. We have recently identified several potential virulence factors co-expressedlco-regulated with the anti-phagocytic capsule of S. zooepidemicus. These include proteins involved in binding of equine plasminogen and in cell division, functions related to .enhanced tissue damaging plasmin activity and rapid bacterial proliferation. We have also cloned and expressed 20 immunoreactive proteins from an expression gene library of a virulent isolate (NC78) of S. zooepidemicus from -outbreaks of equine pneumonia on 24 stables/farms in 1997-98. The library was probed with a pool of convalescent sera from these outbreaks and genes in positive clones identified using the annotated genome sequences of S. zooepidemicus H70 and MGCS10565. The hypothesis that drives this proposal is that the 20 proteins identified by convalescent antibody include.a subset with potential as vaccine components. We plan to express and isolate 9 of these proteins selected on the basis of putative roles and importance as virulence factors. We will then produce antisera specific for each recombinant protein and evaluate the efficacy of the sera in passive mouse protection tests using S. zooepidemicus NC78 and W60 as challenge strains. Inclusion of strain W60, a different strain of S. zooepidemicus will provide information on the cross neutralization ability of antisera. Groups of mice will also be vaccinated with each protein and later challenged with S. zooepidemicus NC78 and W60. Cumulative morbidity/mortality curves will be used to compare relative protective efficacies. The mouse passive protection tests and active immunization/challenge trials will provide information of value in formulation of a novel vaccine to enhance resistance of horses to opportunistic invasion by S. zooepidemicus.