P.aeruginisa

Question 1

1) classification

Answer 1

Family: Pseudomonadaceae
Genus: Pseudomonas
Species: aeruginosa

• nosocomial pathogen
• found on skin flora
• it thrives in moist area so special attention to sinks, water baths, showers etc.

Question 2

2) morphology

Answer 2

Gram negative rods
Arranged in single, pairs or chains (occasionally)
Motile

Question 3

3) growth characteristics

Answer 3

• Facultative anaerobic
• Non-fastidious
• Doesn’t ferment carbohydrate
• Oxidase positive
• catalase positive
• citrate positive
• Grows in 37 to 42 oC:
  It’s growth at 42 oC distinguishes it from other pigment producing Pseudomonas
• Form round smooth fluorescent colonies: pyoverdin
• some strains hemolyse blood

Question 4

4) antigenic structure

Answer 4

• pili (Fimbriae): adhesion to host epithelial cells
• alginate (exopolysaccharide): responsible for mucoid colonies seen in patients with CF
• Lipopolysaccharide (endotoxin property)

Question 5

5) virulence factors

Answer 5

• enzymes
• exotoxins
• endotoxins

Enzymes:
- protease
- elastase 
- neuraminidase
- two hemolysins: 
   Heat Labile phospholipids C
   Heat stable glycolipid 

Exotoxins:

• four type III exotoxins:
  Exoenzyme S, T, U and Y
  Cause cell death or interfere with host immune response to infection
• exotoxin A
  Cause tissue necrosis, by blocking protein synthesis with similar mechanism of action to diphtheria toxin but different structures

Question 6

6) disease

Answer 6

Meningitis 
Pneumonia (especially in CF patient)
UTI 
Sepsis (from would infections; 50% mortality) 
Wound infections (especially burns)

Question 7

7) microbiological diagnosis

Answer 7

Culture:

Blood agar plate:
-multiple colonies with green colour and fruity odour

differential media:
- lactose negative colonies

Infusion broth:
-Oxidase positive

Specific tests:

Does not ferment glucose or lactose- so no reaction on KIA (Kliger iron agar)

Motility

Question 8

8) treatment and prevention

Answer 8

Broad-spectrum penicillin:
Ampicillin or piperacilin

+

Aminoglycoside:
Tobramycin

- nosocomial infection: problem with hospital acquired resistance, due to acquisition of:
Chromosomal beta lactamases
Broad spectrum beta lactamases
Efflux pump 
Porin channel mutation 

Antimicrobial susceptibility tests required