Nutrient Agar preparation???

[dipstickdad]

I purchased a some petri dishes and a bottle of nutrient agar for my son's science fair project. The nutrient agar was made by a company called Pac-Sci (Pacific Science Supplies), and it so happens that they are no longer in business. My problem is that I can't find specific instructions on how to prepare the agar to be able to pour into the petri dishes. The ingredients of the nutrient agar are as follows:
62.5% agar
21.75% peptone, bacteriological
13.05% beef extract, bacteriological
I have read some information about adding gelatin, but I thought that is what the 'agar' component was for. I have also heard about adding sugar, but I thought it already had a nutrient component, hence the name 'nutrient agar'. Additionally, how much water do I use and how do I prepare it? We are doing an experiment on the bacteria that is contained on unwashed fruit vs. washed fruit, if that is helpful. Any advice or instruction that can be given will be appreciated. Thanks in advance for the assistance.

[MaryB]

Hello,

I just want to make sure you are aware of the risks of working with unknown bacteria - please see the following link about “microorganism safety”
https://www.sciencebuddies.org/science- ... fety.shtml

You will likely need to need access to an autoclave (high pressure steam sterilizer) to prepare your nutrient agar. It would be best if your experiment can “be carried out in a professional research setting under the supervision of a competent scientist who understands the risks associated with working with the microorganisms involved” as stated in the “microorganism safety” guidelines.

Mary

[dipstickdad]

Mary-

Thank you for your concern and warnings. We understand the risks and we will be using an abundance of caution while conducting the experiment. However, our main hang-up at this point is knowing how to properly prepare the agar. I have read over several posts and articles on the proper precautionary measures to take in an experiment such as this. What I have had difficulty locating is instruction that applies to how to properly prepare the specific type of agar which I have acquired....which is why I requested this type of information on this post. Again, if anybody can help me with this request I would be grateful. Thanks.

Jason

[sunmoonstars]

Hi Jason,

You said it's a bottle of agar - does this mean it is a liquid? Or does it appear to be a gel right now? In order to be sure the bacteria you grow in your experiment are from the fruit, you need to sterilize (or know it was already sterilized). Is the component list you gave all the information that is on the container?

Tonya

[MaryB]

Jason,

If your agar appears to be a gel you can simply microwave it, but do so with caution. You will want to make sure to do this on LOW power and monitor is closely - you do not want the agar to explode/overflow out of the bottle. Also make sure the lid is loosened. You could start using power level 3 for 5-10 minutes. Be sure to use oven mitts or similar when handling the hot agar and let it sit on the counter to cool before you open it. When the agar cools to the point where you can hold the bottle without burning your hands (~50 degrees C), it is ready to pour. For further info try googling "preparing agar in a microwave" and "tips for pouring agar plates", there are several useful links. An alternate approach is submerge your agar filled bottle in a boiling water bath. See the following link:

http://www.sciencestuff.com/playground/ ... ttle.shtml

I hope this is helpful. Please reply with any questions. Good luck.

Mary

[dipstickdad]

Thanks for trying to assist with my conundrum. The nutrient agar I have is in powder form (10g). For this reason I am unsure if I need to add anything such as gelatin or sugar, and also unsure how much water. There are apparently numerous types of agar, so finding specific instruction for what I have has been difficult. Thanks again.

[MaryB]

Hi Jason,

Just a thought - you can buy pre-poured Nutrient agar plates. See the following link.

http://www.sciencestuff.com/prod/L-p-Agar/1513-10

This may be simpler in the end.

Mary

[sunmoonstars]

Jason, I agree. If you have no idea what it is or how to mix it up, buying the plates is going to be much easier. If you do figure out the instructions, you will need to sterilze the agar before pouring your own plates. This is usually done with an autoclave. I am sure I would NOT do this in my home microwave, gel or fresh liquid. Yuck!

[dipstickdad]

Thanks for the advice. I decided to go ahead and order prepoured dishes. Hopefully they do not go bad in transit! Thanks again.

[deleted-42343]

Science Buddies also has instructions on how to prepare agar plates and how to innoculate them with bacteria:

https://www.sciencebuddies.org/science- ... Agar.shtml

https://www.sciencebuddies.org/science- ... tion.shtml


Good luck!