Which of the following describes Brucella species?

• A. Gram-positive cocci
• B. Spore-forming bacilli
• C. Gram-negative cocci
• D. Small, nonmotile, gram-negative coccobacilli that are facultative intracellular parasites

Answer: (D)

Brucella are tiny gram-negative bacteria that appear as coccobacilli and are nonmotile; they do not form spores. A defining feature is their facultative intracellular lifestyle—they can live outside cells but are capable of invading and replicating inside macrophages, particularly within the reticuloendothelial system. This combination—small size, gram-negative, coccobacillary shape, nonmotile, and intracellular parasites—fits Brucella perfectly. The other descriptions would imply Gram-positive cocci, spore-forming bacilli, or gram-negative cocci, none of which accurately describe Brucella.