This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Bacteriology, Subject name: Microbiology
Most common gram-negative organism in cystic fibrosis is 
Select and explain. 
A. Pseudomonas, B. Escherichia coli, C. Klebsiella, D. Legionella
A: Pseudomonas
Answer: A: Pseudomonas 
Explanation: It occurs in patients with underlying conditions such as cystic fibrosis specially in the Caucasian population