The 3.31-Mb genome sequence of the intracellular pathogen and potential bioterrorism agent, Brucella suis, was determined. Comparison of B. suis with Brucella melitensis has defined a finite set of differences that could be responsible for the differences in virulence and host preference between these organisms, and indicates that phage have played a significant role in their divergence. Analysis of the B. suis genome reveals transport and metabolic capabilities akin to soil͞plant-associated bacteria. Extensive gene synteny between B. suis chromosome 1 and the genome of the plant symbiont Mesorhizobium loti emphasizes the similarity between this animal pathogen and plant pathogens and symbionts. A limited repertoire of genes homologous to known bacterial virulence factors were identified.

Several PCR assays which identify the genus BruceUla but do not discriminate among species have been reported. We describe a PCR assay that comprises five oligonucleotide primers which can identify selected biovars of four species of Brucella. Individual biovars within a species are not differentiated. The assay can identify three biovars (1, 2, and 4) of B. abortus, all three biovars of B. melitensis, biovar 1 of B. suis, and all B. ovis biovars. These biovars include all of the Bruceila species typically isolated from cattle in the United States, a goal of the present research. The assay exploits the polymorphism arising from species-specific localization of the genetic element IS711 in the Brucella chromosome. Identity is determined by the size(s) of the product(s) amplified from primers hybridizing at various distances from the element. The performance of the assay with U.S. field isolates was highly effective. When 107 field isolates were screened by the described method, there was 100% agreement with the identifications made by conventional methods. Six closely related bacteria (Agrobacterium radiobacter, Agrobacterium rhizogenes, Ochrobactrum anthropi, Rhizobium leguminosarum, Rhizobium meliloti, and Rhzodospirillum rubrum) and two control bacteria (Bordeteila bronchiseptica and Escherichia coli) tested negative by the assay.