Science Buddies: "Ask an Expert"

I'm going to make agar plates and determine the viable titer after testing.

I plan on mixing 8.5 ml agar with 0.5 ml soil bacteria dilution in water and 1 ml of a 10^4 dilution of a chemical in distilled water.
Or, if that's too much water, then 9.4 ml nutrient agar with 0.5 ml bacteria dilution and 0.1 ml of a 10^3 dilution of chemical. The entire 10 ml of liquid would be a 10^5 dilution of the chemical.

My directions for making plates says to pour a 3 mm layer on the bottom of the petri dish. Will the bacteria still grow if it is only 1.5-2 mm thick? I don't have enough agar and I can't afford to mess up.
Can I open petri dishes if they have soil microorganisms or would I have to have a lab? I want to gram stain the bacteria.

Thanks for any responses.

Hi,

Please read the Microorganisms Safety Guide: https://www.sciencebuddies.org/science- ... fety.shtmlThe information you need is in the section about Unknown Microorganisms. I do suggest you use a laboratory if you are going to do any staining from your bacterial cultures.

The depth of the agar is important - as long as you cover the bottom and can keep them from drying out during incubation they should grow bacteria without a problem.

good luck! Let me know if you have more questions.

Tonya