Identification and characterization of the Brucella abortus phosphoglucomutase gene: Role of lipopolysaccharide in virulence and intracellular multiplication

Smooth lipopolysaccharide (LPS) of Brucella abortus has been reported to be an important virulence factor, although its precise role in pathogenesis i s not yet clear. While the protective properties of LPS against complement are well accepted, there is still some controversy about the capacity of ro ugh mutants to replicate intracellularly. The B. abortus phosphoglucomutase gene (pgm) was cloned, sequenced, and disrupted. The gene has a high index of identity to Agrobacterium tumefaciens pgm but is not part of the glycog en operon, A B. abortus null mutant lacks LPS O antigen but has an LPS core with an electrophoretic profile undistinguishable from that of the wild-ty pe core, suggesting that glucose, galactose, or a derivative of these sugar s may be part of the linkage between the core and the O antigen. This mutan t is unable to survive in mice but replicates in HeLa cells, indicating tha t the complete LPS is not essential either for invasion or for intracellula r multiplication. This behavior suggests that the LPS may play a role in ex tracellular survival in the animal, probably protecting the cell against co mplement-mediated lysis, but is not involved in intracellular survival.