Brucella spp. are

• A. The etiologic agents of relapsing fever
• B. Small spiral organisms
• C. Intracellular pathogens
• D. Primarily a cause of endogenous human infections

Answer: (C)

Brucella species are intracellular pathogens. They are Gram-negative coccobacilli that invade and survive within host macrophages, multiplying inside phagolysosomes and spreading to organs of the reticuloendothelial system. This intracellular lifestyle underpins the chronic, systemic nature of brucellosis and explains why effective treatment requires antibiotics that penetrate cells and are given for an extended period. They are not the agents of relapsing fever (which are spirochetes like Borrelia), not small spiral organisms, and they are not primarily caused by endogenous human infections.