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PREPARATION OF NUTRIENT AGAR

Bacteriological media come an a wide range of types. Nutrient Agar is a complex

medium because it contains ingredients with contain unknown amounts or types of nutrients.

Nutrient Agar contains Beef Extract (0.3%), Peptone (0.5%) and Agar (1.5%) in water. Beef

extract is the commercially prepared dehydrated form of autolysed beef and is supplied in the

form of a paste. Peptone is casein (milk protein) that has been digested with the enzyme pepsin.

Peptone is dehydrated and supplied as a powder. Peptone and Beef Extract contain a mixture of

amino acids and peptides. Beef Extract also contains water soluble digest products of all other

macromolecules (nucleic acids, fats, polysaccharides) as well as vitamins and trace minerals.

Although we know and can define Beef Extract in these terms, each bach can not be chemically

defined. There are many media ingredients which are complex: yeast extract, tryptone, and

others. The advantage of complex media is that they support the growth of a wide range of

microbes.

Agar is purified from red algae in which it is an accessory polysaccharide (polygalacturonic

acid) of their cell walls. Agar is added to microbiological media only as a

solidification agent. Agar for most purposes has no nutrient value. Agar is an excellent

solidification agent because it dissolves at near boiling but solidifies at 45oC. Thus, one can

prepare molten (liquid) agar at 45oC, mix cells with it, then allow it to solidify thereby trapping

living cells. Below 45oC agar is a solid and remains so as the temperature is raised melting only

when >95oC is obtained.

In this experiment each student will prepare 200 ml of Nutrient Agar to be used in

Experiment 4. In subsequent experiments, the media ingredients can be found in the Appendix.

It is important for you to know how each medium works: what is the energy source? what is the

carbon source? what is the nitrogen source? does the medium have selective or differential

ingredients? why can only some types of bacteria grow on the particular medium?

MATERIALS

1. Electronic or beam balances.

2. Weigh boats, tongue depressors.

3. Tripods, asbestos wire-gauze, asbestos gloves.

4. 10 ml nonsterile pipettes.

5. pH paper or pH meter with standard buffers.

6. 4 13x100 mm screw capped culture tubes.

7. Graduated Cylinder, 250 ml.

8. 2 500ml Erlenmeyer Flasks

9. Beef Extract, Peptone, Agar.

10. 3 N HCl, 3 N KOH.

11. 16 x 150 mm screw cap culture tubes.

12. Nonabsorbent cotton and gauze to make cotton stoppers.

Nutrient Agar

Beef Extract: 0.3%

Peptone: 0.5%

Agar: 1.5%

PROCEDURE

1. You will be making 200 ml of Nutrient Agar. To weigh out Beef Extract, first tare a tongue

depressor, then dip it into the Beef Extract and weigh. Adjust the amount of Beef Extract until

the correct amount is obtained. Be sure to be careful not to get Beef Extract on to the balance!

You need to weight out enough Beef Extract to get a 0.3% solution. Place the tongue depressor

into the flask, beef extract side down.

2. Tare a weigh boat and weigh out enough Peptone and add that to the flask.

3. Add 200 ml of distilled water and swirl to dissolve the peptone and beef extract. Check the

pH, it should be 7.0.

4. Tare a weigh boat and weigh out enough Agar and add that to the flask.

5. With a Bunsen burner, tripod, asbestos wire-gauze, heat the medium to boiling to dissolve the

agar. CAREFUL: 1) keep the rotating the flasks to prevent the agar from cooking onto the

bottom of the flask and 2) watch out: boiling agar can froth and boil out all over the lab bench.

As soon as it begins to boil take it off the heat and put it on to the bench. Allow it to cool a few

minutes.

6. While the agar is still warm, but not hot, pipette 3 ml each into 4 13x100 mm screw cap

culture tubes.

7. Label the flask and your tubes with your name.

8. After preparation of your medium, the instructor will take you to the autoclave.

9. Place your media in the autoclave with those of the rest of the class.

10. After discussion of the parts of the autoclave, autoclave the medium for 20 minutes.

11. The media will be saved and used in Experiment 4.

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12y ago
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12y ago

The nutrient agar plate will serve as a comparison for growth for quality on the MSA plate. Since the MSA plate will favor the growth of gram-positive cocci, you'll be able to see the growth of both gram-negative and gram-positive on the nutrient agar plate.

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9y ago

Agar is made from algae and is used as a from of Gelatin or binder. It was discovered in Japan in the 1650's.

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9y ago

Nutrient agar is used as a test because it is used as a plate for isolation and purification. Nutrient agar is made of beef extract and peptones and it can grow a wide number of organisms.

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12y ago

Agar is simply bacteria food.

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15y ago

agar is the solidifying agent

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12y ago

Nutrient agar is all purpose agar.

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11y ago

because agar is a solidifying agent..

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Q: What purpose does the nutrient agar plate serve?
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What is the purpose of of agar in nutrient agar?

To make it semi-solid


What is the colony color of serratia on nutrient agar plate?

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Will s aureus grow on a crystal violet agar plate?

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because blood agar contain only blood, the culture from the mouth might not grow properly, whereas nutrient agar contain mixture of nutrient and blood, therefore culture from the mouth will properly.


What is the method called when the bacteria sample and nutrient agar are mixed before pouring?

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What is nutrient agar?

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The organism would be expected to grow better in nutrient agar. Nutrient agar is rich in nutrients and microorganisms grow well when there is availability of nutrients.


What is the advantage of using a nutrient agar plate over a nutrient agar slant?

Slants are better suited than agar plates, because they can be capped, preventing the agar and the culture from drying out. The cap also prevents airborne contaminants from entering the slant. Also, slants take up less storage space than an agar plate.


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What is the color of nutrient agar?

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