Toward a feed-based vaccine for bovine pneumonic pasteurellosis: Production of Mannheimia haemolytica antigens in alfalfa.

摘要

Bovine pneumonic pasteurellosis causes serious economic losses in the cattle industry. The primary disease agent is Mannheimia haemolytica A1, a commensal which causes pneumonia when cattle are immunocompromised by stress or disease. Current vaccines require restraints which increase stress. The following investigations were directed toward developing an oral vaccine using transgenic alfalfa plants. The first defined a high-efficiency herbicidal selection system (5 mg/L bialaphos) which will assist future breeding. The next considered a putative adhesin for inclusion in the vaccine. Sequence analyses identified regions homologous to known virulence factors but no conclusive reactions were observed among sera from vaccinated and challenged calves. Finally, optimizations were made to constructs expressing four M. haemolytica antigens to improve accumulation; first by removing cryptic polyadenylation sites (PASs), then by using synthetic genes and additional regulatory elements. No improvements were seen when removing putative PASs, but the latter approach increased accumulation by up to 100-fold.