The correct answer is E. This boy has cystic fibrosis (CF). Patients with CF have bronchiectasis (commonly associated with copious sputum production), recurrent pneumonia, nasal polyps, pancreatic insufficiency, and steatorrhea . Epigastric pain and fat soluble vitamin K deficiency (reflected in the presence of petechiae and purpura) arise as a consequence of pancreatic insufficiency. Patients would also have a history of meconium ileus at birth and lower height and weight (mean 37%) due to malabsorption.
However, the question directly relates to the infectious agent causing the pneumonia: Pseudomonas aeruginosa, an oxidase-positive bacterium with a fruity aroma. Pseudomonas produces blue-green pigments that act as siderophores when grown in an iron-limited environment, but are often colorless on blood agar. P. aeruginosa is an aerobic, Gram-negative rod that produces an exotoxin (exotoxin A) that ADP-ribosylates and inhibits eukaryotic elongation factor-2 (eEF-2), which is a GTP-binding protein involved in the eukaryotic translation of proteins (Corynebacterium diphtheriae also produces an exotoxin with a similar mechanism of action to inhibit protein synthesis). P. aeruginosa is a common pathogen cultured from CF patients.
Activation of macrophages to produce proinflammatory cytokines (choice A) is the mechanism by which lipopolysaccharide (LPS) causes damage. This is endotoxin (an integral component of Gram-negative outer membranes) and is not to be confused with exotoxin.
Blocking release of acetylcholine (choice B) is specific for Clostridium botulinum, which produces a neurotoxin that causes a flaccid paralysis.
Blocking release of GABA and glycine (choice C) is specific for Clostridium tetani, which produces a neurotoxin that causes a spastic paralysis.
Increasing levels of cAMP (choice D) refers to the toxins of enterotoxigenic Escherichia coli (ETEC), Vibrio cholerae, Bordetella pertussis, and Bacillus anthracis. These exotoxins each increase cellular fluid loss, resulting in edema or diarrhea.
MedEssentials (4th Ed.): pp. 536
First Aid (2018): pp. 143.2
First Aid (2017): pp. 139.2
First Aid (2016): pp. 127.2
Pathoma (2018): pp. 91.2
Pathoma (2014-2017): pp. 91.2
Choice A: 15% chose this answer.
Choice B: 2% chose this answer.
Choice C: 2% chose this answer.
Choice D: 19% chose this answer.
Choice E: 62% correctly chose this answer.
- Cystic fibrosis (CF) is identified by the findings of abnormal sputum production and pancreatic insufficiency.
- CF patients suffer from frequent infections with Pseudomonas aeruginosa.
- This bacterium produces exotoxin A, which inhibits eukaryotic elongation factor 2 (eEF-2), inhibiting protein synthesis.
