Pseudomonas

• Pseudomonas are Gram-negative, motile, aerobic bacilli
• They produce water-soluble pigments
• Pseudomonas occur widely in soil, water, plants, and animals
• Pseudomonas aeruginosa is frequently present in small numbers in the normal intestinal flora and on the skin of humans
• Pseudomonas aeruginosa is the major pathogen of the group
• Pseudomonas aeruginosa is widely distributed in nature
• It is commonly present in moist environments in hospitals
• It causes disease in humans with abnormal host defenses
• Pseudomonas aeruginosa is an important nosocomial pathogen
• Obligate aerobe
• Grows readily on many types of culture media
• Produces a sweet or grape-like or corn taco-like odour
• Produces non-fluorescent bluish pigment "pyocyanin", fluorescent greenish pigment "pyoverdin", dark red pigment "pyorubin", or black pigment "pyomelanin"
• Cultures from patients with cystic fibrosis (CF), P. aeruginosa yield mucoid colonies
• Grows well at 37-42°C
• Oxidase-positive
• Does not ferment carbohydrates
• Many strains oxidize glucose
• Antigenic structure and toxins:

  • Pili
  • Polysaccharide capsule
  • Lipopolysaccharide
  • Exotoxin A: extends from cell surface and promotes attachment to host epithelial cells, responsible for mucoid colonies, inhibitor of protein synthesis, causes tissue necrosis, lethal for animals
• Elastase:

  • Causes destruction of elastin-containing tissue
• Alkaline protease:

  • Causes tissue destruction
• Phospholipase C:

  • Acts as a heat-labile haemolysin
• Glycolipid:

  • Acts as a heat-stable haemolysin