Pseudomonas aeruginosa

Overview

Pseudomonas aeruginosa is a species of the pseudomonas genus. It causes opportunistic infections requiring predisposing factors.

Pathogenesis

P.aeruginosa grows on few nutrients and can survive certain disinfectants. The bacteria has toxins and enzymes such as exotoxin A, phospholipase C and proteases that allow tissue invasion and damage. Elastase damages elastin in lung parenchyma and blood vessel walls. P.aeruginosa attaches to host cells via fimbrae and resists phagocytosis and complement via its LPS. It obtains iron from tissues. Mink P.aeruginosa causes haemorrhagic pneumonia and septicaemia in mink with 50% mortality via a secondary thrombocytopenic disease. Cows P.aeruginosa causesBovine mastitis associated with contaminated water used for washing udders; also Metritis, pneumonia, dermatitis and enteritis in cattle. Sheep P.aeruginosa causes Ovine fleece rot, also mastitis, pneumonia and otitis media. Reptiles P.aeruginosa causes necrotic stomatitis in captive reptiles. Pigs P.aeruginosa causes respiratory infections and otitis in pigs. Horses P.aeruginosa causes genital tract infections, pneumonia and ulcerative keratitis in horses. Dogs and cats P.aeruginosa causes otitis externa, cystitis, pneumonia and ulcerative keratitis in dogs and cats. It can also cause deep pyoderma in all species.

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