Pseudomonas aeruginosa

• Causes opportunistic infections requiring predisposing factors
• Pathogenesis:
  • Grows on few nutrients and can survive certain disinfectants
  • Toxins and enzymes such as exotoxin A, phospholipase C and proteases allow tissue invasion and damage
  • Elastase damages elastin in lung parenchyma and blood vessel walls
  • Attachment to host cells via fimbrae
  • Resists phagocytosis and complement via its LPS
  • Obtains iron from tissues
• Clinical infections:
  • Haemorrhagic pneumonia and septicaemia in mink with 50% mortality via a secondary thrombocytopenic disease
  • Bovine mastitis associated with contaminated water used for washing udders; also metritis, pneumonia, dermatitis and enteritis in cattle
  • Ovine fleece rot - suppurative dermatitis after penetration of water into fleece; wool discoloured by pyocyanin pigment; also mastitis, pneumonia, otitis media
  • Necrotic stomatitis in captive reptiles
  • Respiratory infections and otitis in pigs
  • Genital tract infections, pneumonia, ulcerative keratitis in horses
  • Otitis externa, cystitis, pneumonia, ulcerative keratitis in dogs and cats
  • Causes deep pyoderma
• Diagnosis:
  • Specimens should include pus, respiratory aspirates, mid-stream urine and ear swabs
  • Identify colonies on blood and MacConkey agar
  • Oxidative not fermentative
  • Only grow in aerobic conditions
  • Produces diffusable pigments including pyocyanin, a green pigment, and fluorescine
  • Grow on MacConkey agar; colonies have a fruity odour; lactose negative, pale colonies on MacConkey
• Treatment:
  • Multiple antibiotic resistance mediated by large plasmids carrying resistance genes and also chromosomal genes and mutations
  • Gentamicin or tobramycin with carbenicillin or ticarcillin, as well as polymyxin B are effective