The evolution of Brucella as a model intracellular pathogen

ABSTRACT Brucella species are intracellular bacterial pathogens that cause brucellosis, one of the most common zoonoses worldwide. This review traces how Brucella , first discovered in the 19th century through investigations of human and bovine disease, became a modern experimental model system. Work on Brucella has illuminated how intracellular bacteria evade and adapt to host defenses and how they remodel host cell biology to establish a replicative niche. It has also yielded insights that extend beyond pathogenesis into bacterial cell envelope architecture and development. Though long regarded as a small, homogeneous group of mammalian pathogens, the genus has expanded in recent years as “non-classical” Brucella have been isolated from unexpected animal hosts, opening new opportunities to understand the fascinating host preferences and evolutionary history of these closely related Alphaproteobacteria. More than a century after their discovery, Brucella species remain versatile models for the study of intracellular infection, bacterial cell biology, and physiology, and the evolution of host association.