Patent ID: 7416878

Claim:
An immunogenic composition comprising a live Brucella host cell having a rough phenotype, which host cell contains at least two mutations so as to effect sufficient attenuation such that upon exposure to a mammal the host cell will not exhibit full virulence of non-attenuated Brucella , wherein the host cell is transformed with a recombinant DNA construct replicable in Brucella , which DNA construct comprises: (i) a promoter recognizable by Brucella , and (ii) a complementation DNA fragment which encodes a peptide required for lipopolysaccharide O-sidechain synthesis so as to effect lipopolysaccharide O-sidechain synthesis in vivo and which is operably linked to the promoter and which complements a rough-conferring mutation in the host cell, thereby effecting a smooth phenotype in the host cell, wherein the association between the Brucella host cell and the DNA construct is such that following exposure to a mammal the DNA construct gradually separates from the Brucella host cell, whereupon the Brucella host cell reverts to a rough phenotype that is rapidly and safely cleared from the mammal.