Which statement best characterizes C. burnetii?

• A. It is an extracellular rod-shaped bacterium
• B. It is a virus
• C. It is a facultative intracellular bacterium
• D. It is a strict intracellular parasite

Answer: (C)

Coxiella burnetii is best described as a facultative intracellular bacterium. It primarily infects and replicates inside host cells, especially within macrophages, where it resides in a phagolysosome-like compartment and uses the intracellular environment to multiply. At the same time, it can survive outside cells in a hardy, small cell variant form that resists environmental stresses, enabling transmission through the environment (for example, via aerosols). This dual lifestyle—intracellular replication coupled with extracellular environmental persistence—fits the idea of being facultative intracellular. It is not a virus, and it is not purely extracellular or strictly intracellular, hence this description captures its biology most accurately.