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Species of genus Pseudomonas.

Aerobic Gram-negative rod, motile by means of polar flagella. Able to utilise a wide range of nutrients and to grow over a wide temperature range.

Will only grow anaerobically when provided with nitrate.

Will grow readily on a wide range of routine media including bile-containing selective media. Produces irregular irridescent colonies and a distinctive smell.

Oxidase positive and oxidative in the Hugh and Liefson O/F test.

Most strains produce the blue-green pigment, pyocyanin, and a yellow-green pigment, pyoverdin. Pigment production is enhanced by King's A + B.

P. aeruginosa is an opportunistic pathogen which can infect almost any body part. It is a major cause of infection in patients with burns or cystic fibrosis and can cause pneumonia in intubated patients. It is spread through contact.

It can also cause urinary tract infection, septicaemia, osteomyelitis and endocarditis.

Occurs in the gut of a small percentage of people, with a higher incidence in hospital in-patients.

A number of virulence factors are associated with P. aeruginosa:

  • Endotoxin
  • Exotoxin A
  • Extracellular proteases
  • Extracellular elastases
  • Extracellular slime
  • Pyocyanin
  • Pyoverdin

Exotoxin A acts as an inhibitor of elongation factor in eukaryotic protein synthesis. Exotoxin A has been shown to have an action similar to diphtheria toxin, transferring the ADP-ribosyl portion of NAD+ to elongation factor 2. However, the toxins have different receptors as shown by the fact that mice or rats are naturally resistant to diphtheria toxin but susceptible to Exotoxin A.

The extracellular proteases and elastases breakdown tissues at the site of infection.

The extracellular slime helps to prevent phagocytosis.

Pyocyanin is exerts an antimicrobial effect, helping to prevent competition with other organisms at the site of infection.

P. aeruginosa has a outer cell-wall which excludes various antibacterials, it is only susceptible to aminoglycosides and newer beta-lactams (carbenicillin, acylureidopenicillins, third generation cephalosporins and imipenum).

Medical Microbiology. Mims, C. et al Mosby 1993
Biology of Microorganisms. Brock et al. Prentice Hall International. 1994

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