Brucella attenuation and relevance to vaccine properties

Brucellosis is a zoonotic disease caused by Gram negative, facultative intracellular bacteria. The genus includes six species, the major three being Brucella melitensis, B. abortus and B. suis. These three species cause abortions in their primary livestock hosts resulting in major economic losses worldwide. Although attenuated live vaccine strains have been derived from the three important species and used extensively, there have been adverse side-effects. To study the virulence properties of Brucella, we targeted intracellular survival genes using macrophage survival and mouse virulence. We first evaluated the method using B. abortus 2308 wild type strain. Brucella genes were randomly inactivated following electroporation with a DNA construct that included a transposon element associated with antibiotic resistance marker. Transformed clones were then screened for survival in mice or in monocyte-derived macrophages, and were compared with the parental wild type strain. Clones showing reduced survival in the mouse or the macrophage model, respectively, were considered deleted in an essential virulence gene. In an alternative approach the B. melitensis vaccine strain Rev. I has been compared to its wild type prototype strain, B. melitensis 16M. The study included 2-D gel analysis of the protein profiles of these strains reveal similar patterns when grown under normal growth conditions. Electron microscopic comparison has shown, however, that strain Rev. I changes its ultrastructural morphology according to the surrounding environmental conditions. (C) 2002 Elsevier Science B.V. All rights reserved.