Brucella spp. are facultatively intracellular bacteria that persist and multiply in the macrophages of their mammalian hosts. The so-called phagosome to which they have adapted is their natural living niche VSports手机版. Characterization of this niche would facilitate an understanding of the true relationship between the host cell and the intracellular bacteria. This Opinion analyses and discusses the characteristic properties and genesis of this vacuole during phagocytosis as deduced from the virulence factors necessary for intracellular multiplication of the pathogen. We conclude that the replicative niche of Brucella spp. --the 'brucellosome'--differs from all other cellular organelles, and that it isolates the pathogen from certain cytoplasmic nutrients. Adaptation to the stress conditions encountered and the use of anaerobic respiration enable brucellae to replicate in the compartment they create. .