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: Medicine
Gram staining of the sputum of the patients with pneumonia is diagnostic with all these pathogens, EXCEPT: 
Select and explain. 
A. S. pneumoniae, B. S. aureus, C. Gram-negative bacteria, D. Coxiella burnetii
D: Coxiella burnetii
Answer: D: Coxiella burnetii 
Explanation: Gram's staining may identify ceain pathogens (e.g., S. pneumoniae, S. aureus, and gram-negative bacteria) by their characteristic appearance. A sputum sample must have 1. >25 neutrophils 2. <10 squamous epithelial cells per low-power field, to be adequate for culture. Ref: Harrison, E-18, P-2133