Pseudomonas

GENUS Pseudomonas

This genus contains a large number of species, a few of which are human pathogens, some are animal pathogens and others are important pathogens of plants. Species also widely distributed and may contaminate the hospital environment and cause opportunist infections. Most important species in humans are P. pseudomonas and P. mallei.

 

Pseudomonas aerugenosa

Characteristics:

Aerobic Gram-negative rod, motile by means of polar flagella. Able to utilize a very wide range of carbon and energy sources and to grow over a wide temperature range. Does not grow anaerobically.

 

Transmission:

Carriage as part of the normal gut flora occurs in a small percentage of normal healthy people and in a higher proportion of hospital inpatients. Thus endogenous infection may occur in compromised patients. P. aerugenosa is widespread in moist areas in the hospital environment; patients usually become infected by contact spread, directly or indirectly, from these environmental sites.

 

Diseases:

  • P. aerugenosa is an opportunist pathogen that can infect almost any body site given the right predisposing conditions.
  • It causes infections of skin and burns; it is a major lung pathogen in cystic fibrosis and can cause pneumonia in intubated patients.
  • It can also cause:
    • urinary tract infections,
    • septicemia,
    • osteomylitis and
    • endocarditis.

 

LABORATORY DIAGNOSIS:

Sample Collection:

Samples ( pus, swab, sputum)  are collected from the site of infection either by swab or in sterile container

 

Methods for Identification of Organism:

  1. Microscopy: Gram-negative motile rod.
  2. Culture: Nutrient agar, MacConkey agar & Cetrimide agar (Selective Media)
    • Nutrient agar:  Bluish green colonies due to pigment production by bacteria. 
      • Other types of pigment produced:
        • Green blue (pyocyanin),
        • yellow-green  pigment (pyoverdin),
        • red ( pyorubin) and
        • black( pyomelanin).
    • MacConkey agar:  Colonies are colorless and nonlactose fermenter (NLF).

 

  1. Biochemical Reactions:

Oxidase test               –   Positive

Citrate utilization test –   usually  Positive

TSI agar slant:               Red /Red(no reaction)

     

 4.  Antibiotic sensitivity test:

One of the most notorious organism for multi drug resistence. It intrinsic resistence to many antibiotic like Cotrimoxazole, Tetracycline, Chloramphenicol etc.