Desarrollo de nuevas vacunas frente a brucella ovis: estudio de genes implicados en la síntesis del núclo del lipopolisacárido

Abstract

Brucella ovis produces a disease that affects sheep causing great economic losses. The only existing vaccine consists of live strain B. melitensis Rev 1. However, due to its ability to cause abortions in cattle, its infectivity in humans and its interference in the diagnosis of B. melitensis, Rev1 employment is prohibited in many areas where B. melitensis has been eradicated. In many of these areas, however, there is a high prevalence of B. ovis. Therefore, the development of new vaccines against infection by B. ovis is a must.

Lipopolysaccharide (LPS) is a virulence factor in Brucella. Recently it has been shown that the core of the LPS of B. abortus and B. melitensis is a branched structure, and at least three glycosyltransferases, wadA, wadB and wadC have been described to be involved in its synthesis. The present work found that these three genes are highly conserved in the species B. ovis. While mutation in the gene wadA in B. ovis did not generate alterations in the properties of the cell envelope and did not affect its survival in the murine model, wadB and wadC were involved in the synthesis of the core LPS of B. ovis. Furthermore, mutants wadB and wadC were attenuated and protected from an experimental B. ovis infection in the mouse model. The mutant wadB was the most effective, surpassing even the vaccine strain Rev 1.

In silico analysis of genes related to the synthesis of LPS sequences allowed to observe a very high homology between them, greater than initially predicted. The sequence analysis showed that the mutation in the pseudogene manBcore, which generates a loss of two functional domains essential for the enzymatic activity is specific to B. ovis. In addition, B. ovis manBO-Ag gene deficiencies generated in the core of LPS caused alterations in the properties of the outer membrane. The sequence of manBO-Ag gene was identical in all strains of B. ovis studied except B. ovis REO. It is likely that the B. ovis manBO-Ag gene may be supplying manBcore gene activity. The strain B. ovis REO is recommended to obtain the antigen for the diagnosis of B. ovis. When compared with the strain B. ovis PA, differences in the cell envelope properties were found, compatible with the deletion of the gene manBO-Ag.