Identification of genes required for chronic persistence of Brucella abortus in mice

The genetic basis for chronic persistence of Brucella abortus in lymphoid o rgans of mice, cows, and humans is currently unknown. We identified B. abor tus genes involved in chronic infection, by assessing the ability of 178 si gnature-tagged mutants to establish and maintain persistent infection in mi ce. Each mutant was screened for its ability to colonize the spleens of mic e at 2 and 8 weeks after inoculation. Comparison of the results from both t ime points identified two groups of mutants attenuated for chronic infectio n in mice, The first group was not recovered at either 2 or 8 weeks postinf ection and was therefore defective in establishing infection. Mutants in th is group carried transposon insertions in genes involved in lipopolysacchar ide biosynthesis (wbk4), in aromatic amino acid biosynthesis, and in type T V secretion (virB1 and virB10). The second group, which was recovered at wi ld-type levels 2 weeks postinfection but not 8 weeks postinfection was able to establish infection but was unable to maintain chronic infection. One m utant in this group carried a transposon insertion in a gene with homology to gcvB of Mycobacterium tuberculosis, encoding glycine dehydrogenase, an e nzyme whose activity is increased during the state of nonreplicating persis tence. These results suggest that some mechanisms for long-term persistence may be shared among chronic intracellular pathogens. Furthermore, identifi cation of two groups of genes, those required for initiating infection and those required only for long-term persistence, suggests that B. abortus use s distinct sets of virulence determinants to establish and maintain chronic infection in mice.