9.6 Nutritional Requirements and Media

Selective media

Contains nutrients that encourage growth of certain microbes.

Differential media

Media that can further differentiate based on salinity, fermentation, pH, etc.

Fastidious organisms

Organisms that need very specific nutrients.

Blood agar

Many fastidious organisms require this type of media.

Alpha hemolysis (α)

Hemoglobin is reduced causing browning; e.g., Streptococcus pneumoniae.

Beta hemolysis (β)

Complete lysis of RBC creating a clearing zone; e.g., Streptococcus pyogenes.

Gamma hemolysis (γ)

Growth occurs but there is no hemolysis or reduction.

Mannitol Salt Media

Selects and differentiates pathogenic & non-pathogenic Staphylococci.

MacConkey Agar

Selects and differentiates Gram negative & lactose fermenters.