Agar and Petri dish help!?

Question

I need to perform my science fair experiment over winter break. So I cleared it with my teacher and brought home the equippment. I made 60 Petri dishes of agar and they are in my refridgerator. They're not setting up though. This might be because I cooked the agar in the microwave with the water, instead of boiling the water and then dissolving the agar in it. It's been 24 hours now, and they're not really setting up. Any advice?

I definitely had the right amount of water.

Answer 1

Hmmm, what kind of agar was it? Anything else in the solution (for most bacteria to grow they will want some sort of nutrient base).

If it came to a complete boil in the ,microwave it should be totally fine (it is what we do in lab for gels all the time) and should set up as soon as it cools.

I know you feel confindent about the concentration of agar used but for a typical 1% solution it is 1gram agar/100ml of solution.

Like I said earlier though most bacteria or fungi will want specialized media like basic nutrient agar, blood agar, or tryptic soy agar (TSA) or at very minimum you need to make your agarose in a buffered solution (like buffered saline= 0.9%NaCl).

If you have more agar I would carefully weigh out more and boil it entirely then LET IT COOL IN THE BOTTLE to make sure it solidifies. If this works, reheat it (it will melt very quickly) and pour out plates.

If it doesn't solidify again I would find a new source for agar.
Good Luck

Answer 2

I would say its because it wasnt properly mixed. Are you sure you added the correct amount of "agar" not the nutrients? If you added too much water, and not enough agar then it also would not set up properly. When done properly agar will "set" in 5 minutes. It then would need to be refrigerated for 24 hours. I also dont think a microwave was the best choice, you need to sterilize the agar before pouring the plates. A microwave wont cut it. When you actually pour the plates the entire area needs to be sterile, we have 2 meeker burners going around the plates to sterilize the area, in order for the plates to not have any contamination.

Answer 3

Double check the amount of water that was supposed to be mixed with the agar. If that amount was right, then the only way you may be able to salvage your materials is to re-cook the agar on the stove top. I don't guarantee that that will work, but you are probably desperate. You will need to sterilize the agar in a pressure cooker if you are growing bacteria.

Answer 4

Microwaving or boiling doesn't make any difference. You don't have the right concentration of agar, that's all. You will have to make new plates.

Answer 5

A petri dish is a vessel to enclose the sample of microorganism. The agar medium is the medium the microorganism is grown in.