Pseudomonas aeruginosa

Categorization
Cell Wall: Gram Negative Shape: Rod
Metabolism: Obligate Aerobe Biochemistry: Lactose Non-fermenter, Oxidase Positive
Culture and Detection
  • P. aeruginosa produces a characteristic pigment which gives colonies a greenish/bluish color. The organisms also give off a characteristic fruity odor.
Transmission
  • P. aeruginosa is widely distributed, especially in moist environments. The organism generally only colonizes humans who have globally reduced immunity or local reductions in immunity due to trauma.
Virulence Factors
  • Pili:
    • Allow for adherence to injured cells.
  • Exotoxins:
    • P. aeruginosa secretes a variety of exotoxins which enhance virulence. Notably, Exotoxin A inhibits protein synthesis but with a mechanism distinct from Diptheria Toxin.
Clinical Consequences
  • Overview
    • P. aeruginosa can infect nearly any tissue in the body. Thankfully, most infections are rare in healthy individuals and occur almost exclusively in hospitalized patients, immunocompromised patients, or those with localized injuries.
  • Bacteremia and Sepsis
    • May occur in ICU patients or burn patients and has a high mortality.
  • Hospital-acquired Pneumonia
  • Urinary Tract Infection
    • UTIs usually occur in those with foley catheters.
  • Infective Endocarditis
    • Pseudomonal infective endocarditis can be observed in IV drug abusers and takes on a "Subacute" picture, affecting the right heart.
  • Osteomyelitis
    • Pseudomonal osteomyelitis can occur when bacteria can spread to bone from localized infections and tends to affect the vertebrae. In IV drug abusers spread is usually from infective endocarditis. In children spread is usually from puncture wounds to the foot whereas in elderly patients spread is usually from a UTI.
  • Skin Infections
    • Dermatitis usually occurs in burn patients and may lead to bacteremia and sepsis.
  • Ear Infections
    • Swimmer's Ear: May occur in healthy patients and is usually a mild superficial infection
    • Malignant Otitis Externa: Usually occurs in elderly suffering from Diabetes Mellitus in which infection spreads through the ear canal and invades the mastoid bone.
  • Corneal Infections
    • Usually occurs due to corneal trauma associated with wearing contact lenses. Infection can spread rapidly and if left untreated can lead to blindness.
Treatment
  • Pseudomonas is notoriously resistant to many antibiotics. Often piperacillin is used and occasionally an aminoglycoside is added.