A 14 year old girl with cystic fibrosis is admitted to the hospital with fever and shoness of breath, and is diagnosed with pneumonia. During a respiratory therapy session, she coughs up mucus that is distinctly greenish in color. Which of the following organisms should be suspected?

The clues suggesting infection with Pseudomonas aeruginosa are the green-tinged sputum (due to the formation of blue and green pigments by P. aeruginosa), and the association with cystic fibrosis. Unfounately, P. aeruginosa is very difficult to treat with most antibiotics, and presents a very difficult therapeutic challenge in the management of cystic fibrosis patients. Klebsiella pneumoniae is most often seen in alcoholics, the elderly, and diabetics. Mycoplasma pneumoniae is a common cause of community-acquired atypical pneumonia, and is characterized by a dry, non-productive cough. Pneumocystis carinii usually causes pneumonia in immunocompromised patients, e.g., AIDS patients. Ref: Brooks G.F. (2013). Chapter 16. Pseudomonads, Acinetobacters, and Uncommon Gram-Negative Bacteria. In G.F. Brooks (Ed), Jawetz, Melnick, & Adelberg's Medical Microbiology, 26e.