The genetic diversity of Brucella species

How to define the Brucella genus has been debated for several decades. Due to the limited variation in the genome, including no variation in the 16S rRNA gene—a traditional marker for species identity in bacteria—some researchers have considered there to be only one species. In this chapter, we discuss the techniques used to assess the genetic diversity of Brucella, along with the process of evolution of this genus and its differentiation from Ochrobactrum sp. Among the most relevant aspects regarding the evaluation of the Brucella genome, we highlight the division between classical (or core) and atypical species and strains; their similarities and differences; and the application of knowledge of this diversity as a tool to aid diagnosis, identify epidemiological links, trace pathogen migration patterns over the centuries, and resolve outbreaks with control and prevention measures. More and more hosts are recognized as potential reservoirs of Brucella spp. New species have been extensively described in recent years, thanks to advances in whole-genome sequencing technologies, which have expanded the frontiers of knowledge about this very peculiar pathogen.