Pseudomonas aeruginosa: Overview

Summary

Pseudomonas aeruginosa are gram-negative, rod-shaped, and encapsulated bacteria, with colonies that have a grape-like odor. Pseudomonas is also catalase and oxidase positive. Virulence factors of this bacteria include its production of Exotoxin A, which inhibits elongation factor 2 via ADP ribosylation. Another virulence factor produced by Pseudomonas aeruginosa are pyoverdine and pyocyanin, blue-green pigments that help the bacteria scavenge iron from its local environment.

Key Points

• Pseudomonas aeruginosa overview 
  • Characteristics
    • Gram negative rod
      • Have a motile appearance on microscopy
    • Oxidase +
    • Encapsulated
      • Higher risk of severe infection in asplenic patients (prior surgery, sickle cell)
    • Catalase +
    • Non-lactose fermenting
    • Has a grape-like odor
    • Aerobic
    • Biofilm formation may contribute to pneumonia in cystic fibrosis
  • Virulence Factors
    • Exotoxin A
      • inactivates EF-2 (elongation factor) via ADP ribosylation
      • inhibits protein synthesis at the ribosome, since EF-2 is needed to translocate tRNA to allow peptide elongation
      • Similar mechanism to diphtheria toxin (Corynebacterium diphtheriae)
    • Pyoverdine and pyocyanin
      • blue-green pigment often seen on microscopy
      • Generates reactive oxygen species
    • Phospholipase C
      • Breaks down phospholipids to degrade cell membranes
    • Endotoxin
      • Causes fever, shock, and DIC in patients
      • Seen in all gram-negative bacteria due to LPS in the bacterial membrane
    • Elastase
      • Breaks down elastin
      • Important for blood vessel and connective tissue destruction (e.g. ecthyma gangrenosum)