A 9-year-old boy with cystic fibrosis a genetic disease that causes a number of problems, including the buildup of thick sticky mucus in the lungs—complained of increasing fatigue, shortness of breath, and worsening cough. When his mother took him to the doctor, she mentioned that his cough was productive, meaning that it contained sputum (pronounced spew-tum ). She was particularly concerned that the sputum was a blue-green color. His doctor immediately suspected a lung infection by Pseudomonas aeruginosa, a common complication of cystic fibrosis. A sputum sample was collected and sent to the clinical laboratory.  In the clinical laboratory, the sample was plated onto MacConkey agar and blood agar and incubated. Mucoid colonies surrounded by a bluish-green color grew on both types of agar media. The colonies on MacConkey had no pink coloration, so the medical technologist concluded that the cells did not ferment lactose. She noted the blue-green color on the agar plates and in the sputum, knowing that P. aeruginosamakes several pigmented compounds that give rise to colors ranging from yellow to blue. One of the pigments functions as a siderophore, which is a molecule that binds iron. Another is a quorum-sensing signal that helps the bacterium regulate biofilm development. Further testing showed that the bacterium was an oxidase-positive, Gram-negative rod, consistent with the physician’s initial suspicions. The patient was treated with antibiotics, with only limited success. Like most cystic fibrosis patients, he developed a chronic lung infection that continued to require repeated treatment.

 1. What role did cystic fibrosis play in the disease process?

 2. What is the significance of the colonies being mucoid?

 3. How would the siderophore (the iron-binding compound) benefit the bacterium?

 4. Why would the boy’s lung infection make his pre-existing respiratory problems even worse?