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.
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.
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.
Agar is simply bacteria food.
agar is the solidifying agent
Nutrient agar is all purpose agar.
because agar is a solidifying agent..
Yes. S. aureus can grow on TSA plate because this plate is general purpose medium and has most nutrient for bacteria growth.
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.
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.
Nutrient agar is a clear pale buff colour.
simply agar medium
To make it semi-solid
Yellowish
Yes. S. aureus can grow on TSA plate because this plate is general purpose medium and has most nutrient for bacteria growth.
whitw to whitish gray
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.
Pour plate method
simply agar medium
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.
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.
nutrient agar is used generally for culturing any organism.But Muller hinton agar is specifically used for testing antibiotic sensitivity as it does not contain any inhibitory substances for the growh of the organism
Nutrient agar is a clear pale buff colour.
simply agar medium