Agar
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Agar polymer consisting of galactose (sugar) subunits. It is most commonly used in laboratories, after being dissolved in boiling water and cooled.[1] Once prepared, if is usually a gelatinous substance (although sometimes it is kept liquid) which is ideal for growing microorganisms. The agar gel is usually placed in a Petri Dish (or Petri Plate), and inoculated with one or more bacterial or fungal samples.[2]
Agar is also digestible to mammals including humans, so it can also be used in cooking. For this purpose, it is usually sold as flakes, powder, or a bar. [3][4]
Types of laboratory agar
A variety of agar types have been developed for various purposes.
| Type | Description | Uses |
|---|---|---|
| Luria Bertani Agar | Non-selective nutrient | Suitable for growing almost any bacteria, as long as any other requirements are met. |
| Blood Agar | Contains animal blood cells | Can restrict live culture to bacteria which can consume and live on blood |
| Chocolate Agar | Contains sheep blood which can provide the X and V factors necessary for Haemophilus[1] | Good for culturing fastidious organisms such as Haemophilus species and Neisseriagrowth[1] |
| MacConkey Agar | Selective medium which only grows Gram-negative bacteria | |
| Miller's LB Agar | Very similar to Luria Bertani, but contents are in different proportions[1] | |
| Neomycin Agar | ||
| Non-nutrient Agar | Contains no usable nutrience | Cannot feed bacteria, but can be used as a medium for other microorganisms. |
| Nutrient Agar | Offers plentiful, easily-consumed nutrience[1] | Can grow a wide variety of bacteria and fungi[1] |
| Sabouraud Agar | ||
| Thayer-Martin Agar | Chocolate agar designed to isolate gram-negative Neisseria gonorrhoeae[1] | Used to test for Gonorrhea-causing bacteria[1] |
| Tryptic Soy Agar | Generic nutrient usable by many microorganisms | Good for studying colony morphology, development of a pure culture (by eliminating microorganism contamination), and simply expanding the sample size for further testing[1] |
| XLD Agar |