Haemophilus influenzae diagnosis using Satellite Test

 

  • Haemophilus spp does not grow on 5% Sheep Blood Agar, which contains hemin (factor X) but lacks NAD (factor V).
  • Haemophilus influenzae will grow in the hemolytic zone of Staphylococcus aureus on blood agar plates because staphylococcus aureus produce NAD as a metabolic byproduct when grow in a culture media.
  • H. influenzae will not grow outside the hemolytic zone of Staphylococcus aureus. This is known as satelliting.
Haemophilus influenzae Satellitism Test

Haemophilus influenzae Satellitism Test

 

Satelliting Test Procedure:

  1. Mix a loopful of suspect Haemophilus growth in 2 ml of sterile saline or sterile peptone water, make sure none of the chocolate agar medium is transferred with it.
  2. Using sterile swab, inoculate the organism suspension on a plate of nutrient agar and a plate of blood agar.
  3. streak a pure culture of S. aureus across each of the inoculated plates.
  4. Incubate both plates in a carbon dioxide enriched atmosphere at 37C for 18 hours.
  5. Examine the cutlures for growth and satellite colonies.

Result Interpretation:

  • H. influenzae: shows growth on the blood agar plate but NOT on the nutrient agar plate, and the colonies near the column of S. aureus growth are larger than those far from it.
  • If satellite colonies are present on both plates the organism is probably Haemophilus species that requires only Factor V (NAD) such as H. parainfluenzae.

Reference:
District Laboratory Practice in Tropical Countries, Part 2, second edition


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