This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Microbiology
Which of the following is an obligate intracellular parasite? 
Select and explain. 
A. Tropheryma whippelii, B. Baonella henselae, C. Ehrlichia chaffeensis, D. Coxiella burnetii
C: Ehrlichia chaffeensis
Answer: C: Ehrlichia chaffeensis 
Explanation: Ans: C. Ehrlichia chaffeensis (Ref: Ananthanarayan 10/e p416, 8/e p409; Jawetz 27/e p346, 347; Harrison 19/e p1159, 1162)Though both Coxiella and Ehrlichia are obligate intracellular pathogens, in 2009 scientists repoed a technique allowing the Q-fever pathogen Coxiella burnetii to grow in an axenic culture and suggested the technique may be useful for study of other pathogens.Hence, Ehrlichia is a better answer in this case.