In cystic fibrosis the most common organism which causes infection is
**Core Concept**
Cystic fibrosis is a genetic disorder characterized by abnormal chloride ion transport across epithelial membranes, leading to thickened mucus production. This mucus buildup affects various organs, including the lungs, pancreas, and digestive system, making these individuals susceptible to recurrent respiratory infections.
**Why the Correct Answer is Right**
The most common organism causing infection in cystic fibrosis patients is *Pseudomonas aeruginosa*. This bacterium thrives in the thick, dehydrated mucus environment of cystic fibrosis patients, leading to chronic lung infections. The pathogenesis involves the bacterium's ability to form biofilms, which protect it from antibiotics and the host's immune system. The defective cystic fibrosis transmembrane conductance regulator (CFTR) protein leads to increased sodium absorption, causing water to be reabsorbed, resulting in dehydrated mucus that facilitates the colonization of *Pseudomonas aeruginosa*.
**Why Each Wrong Option is Incorrect**
* **Option A:** *Staphylococcus aureus* is a common cause of skin infections but is not the most common organism causing infection in cystic fibrosis patients.
* **Option B:** *Haemophilus influenzae* is a common cause of respiratory infections in children but is not as prevalent in cystic fibrosis patients as *Pseudomonas aeruginosa*.
* **Option C:** *Escherichia coli* is a common cause of urinary tract infections but is not typically associated with cystic fibrosis respiratory infections.
**Clinical Pearl / High-Yield Fact**
Recurrent respiratory infections in cystic fibrosis patients are often caused by the same organism, which can lead to the development of chronic infections and antibiotic resistance. Regular pulmonary function tests and chest imaging are essential for monitoring and managing these patients.
**Correct Answer:** C. *Pseudomonas aeruginosa*.