Most strains of Haemophilus spp does not grow on 5% Sheep Blood Agar, which contains hemin (factor X) but lacks NAD (factor V).

Staphylococcus aureus produce NAD as a metabolic byproduct when grow in a  culture media containing blood . Therefore, Haemophilus spp may grow on sheep blood agar very close to the colonies of Staphylococcus aureus (as it produces NAD-factor V); this phenomenon is known as satelliting.

Why Haemophilus needs X and V Factor? 

Haemophilus influenzae uses factor X to produce essential respiratory enzymes such as cytochromes, catalases and peroxidase.  Factor V is used as an electron carrier in the organism’s oxidation-reduction system.

Satellitism test for the identification of Haemophilus influenzae

Satellitism test for the identification of Haemophilus influenzae

Procedure of Satellitism test to identify Haemophilus influenzae

  1. Mix a loopful of suspected colonies of Haemophilus colonies in about 2 ml of sterile physiological saline (or sterile peptone water). Make sure none of the Chocolate agar medium is transferred.
  2. Using a sterile swab, inoculate the organism suspension on a
    a. Plate of nutrient agar or tryptic soya agar
    b. 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 carbondioxide enriched atmosphere at 35 to 37oC for 18-24 hours.
  5. Examine the culture plates for growth and satellite colonies

Observation and interpretations

The suspected colonies are of Haemophilus influenzae if:

  1. Growth is seen in the blood agar but not in the nutrient agar (or tryptic soya agar) plate
  2. The colonies near the column of S. aureus growth are larger than those furthest from it

If satellites colonies are present on both blood and nutrient agar plates than the organism is probably a Haemophilus species that requires only factor V, such as H. parainfluenzae.

Note: Very occasionally satellitism is shown by strains of Neisseria, Streptococcus species and diphtheroids.

Interesting Fact:
Haemophilus influenzae is the first free-living organism to have its genome (complete genetic code) sequenced

Tankeshwar AcharyaBacteriologyBacteriology Notelaboratory diagnosis of Bacterial Disease
Most strains of Haemophilus spp does not grow on 5% Sheep Blood Agar, which contains hemin (factor X) but lacks NAD (factor V). Staphylococcus aureus produce NAD as a metabolic byproduct when grow in a  culture media containing blood . Therefore, Haemophilus spp may grow on sheep blood agar very...
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Tankeshwar Acharya

Hello, thank you for visiting my blog. I am Tankeshwar Acharya. Blogging is my passion, I am working as a lecturer and Microbiologist at Department of Microbiology and Immunology, Patan Academy of Health Sciences, Lalitpur. If you want me to write about any posts that you found confusing/difficult, leave in the comments below.

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