What type of organism is Coxiella burnetii?

• A. Intracellular, gram negative bacteria
• B. Gram negative intracellular bacteria
• C. Gram positive cocci
• D. RNA virus

Answer: (B)

Coxiella burnetii is a bacterium with a Gram-negative cell envelope that lives and replicates inside host cells (an obligate intracellular organism). That combination—Gram-negative cell wall plus intracellular lifestyle—best describes its biology. It is not a Gram-positive organism, and it is not a virus, since it has bacterial characteristics and replicates within cells rather than as a standalone viral particle.