C. burnetii is a bacterium with which characteristics?

• A. Gram-positive spore-forming rod
• B. Obligate intracellular coccobacillus
• C. Obligate extracellular cocci
• D. Facultative intracellular coccobacillus

Answer: (D)

Coxiella burnetii shows a dual lifestyle: it can survive outside cells and also replicate inside cells, so it’s best described as a facultative intracellular coccobacillus. In the environment, it forms environmentally resistant small cell variants that endure desiccation and aerosols, which helps transmission. Inside a host, it is taken up by macrophages and replicates within acidic phagolysosomes, producing large cell variants that drive intracellular growth. It’s a Gram-negative, pleomorphic coccobacillus, not a Gram-positive spore-forming rod and not strictly extracellular or strictly intracellular. That combination of extracellular survival and intracellular replication is why the facultative intracellular description fits best.