Brucella spp. are best described as which type of organism?

• A. Gram-positive cocci
• B. Facultative intracellular coccobacilli
• C. Spirochetes
• D. Obligate extracellular rods

Answer: (B)

Brucella are small Gram-negative bacteria with a coccobacillary shape that behave as facultative intracellular pathogens. This means they can invade and replicate inside host cells, especially macrophages, allowing them to persist and disseminate within the reticuloendothelial system. That intracellular lifestyle is what distinguishes them from organisms that live only outside cells. They are not Gram-positive cocci, nor spirochetes, and they are not obligate extracellular organisms, since they thrive inside cells as part of their infection strategy. Therefore, Brucella species are best described as facultative intracellular coccobacilli.