What type of organism is described as facultative intracellular and very virulent?

Brucella spp. are classified as facultative intracellular organisms, meaning they can survive and replicate within the host's cells, particularly inside macrophages. This ability to thrive within the immune cells enables them to evade the host's immune response, making them particularly virulent. Brucella species are known to cause brucellosis, which can lead to serious health issues in humans, including fever, sweating, malaise, and in chronic cases, more severe complications.

The virulence of Brucella spp. is significantly attributed to their ability to manipulate host cellular mechanisms to gain a niche where they can avoid detection and destruction by the immune system. This intracellular lifestyle directly contributes to their pathogenicity and the persistence of infection in the host.

Other options mentioned do not exhibit the same level of virulence combined with the facultative intracellular lifestyle seen in Brucella spp. Acinetobacter spp., for example, are primarily environmental organisms known for their antibiotic resistance but do not exhibit the same intracellular capabilities or virulence associated with Brucella. Stenotrophomonas maltophilia, while opportunistic, tends to act as an extracellular pathogen, and Bordetella pertussis is specific for targeting epithelial cells, mainly in the respiratory tract