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Monday, October 18, 2004

Choosing the appropriate agar

Agar (or medium) is a gel-like polysaccharide used as a thickening agent to grow microorganisms. There are several types for different uses.

Complex- Has a variety of ingredients.
Defined- Pure chemicals within the mixture. They also need a buffer added to them.(Good source for anti-microbial requirements, AKA growth factors)
Selective - Helps to narrow down organism of interest. EX: Glucose salts.
Thayer-Martin - Isolates N.Gonorrhea, Antibiotics will inhibit growth of fungi, Gram positive and Gram negative rods, and will allow growth with little competition.
Differential- Created in mind that different organisms metabolize different materials in different ways. A bacteria type can change a substance in a recognizable way. EX: Blood agar- "strep test"
Glucose Salts - Only organisms that can make all cellular components from glucose and inorganic salts are able to grow.
Trypicase-Soy - Organisms must require vitamins and growth factors in order to grow on this agar.
EMB (Eosin Methylene Blue) - A selective medium that permits Gram-negative rods to grow, but inhibits Gram-positive bacterial growth.

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