Growing bacteria at home

[deleted-163597]

One of my experiments for my science fair project is to grow bacteria, I'm testing it for something, but first I need them to start growing. I'm honestly now sure what I'm doing wrong. I bought agar I had to prepare myself and when I first started my experiments last Saturday, I prepared it wrong. When I realized my mistake on Tuesday, I prepared it again (right this time). I collected bacteria from my laptop and door handle (there was plenty of dirt on the swabs from my laptop) and transferred the samples to my agar (without tearing it, i took precaution). I stored the samples inside a plastic bag and put them upside down in a warm dark place. Now that it's Thursday, I'm still not seeing any sign of growth. Am I doing something wrong? I'm just not sure. My two other experiments are going very well, just this one is wrong. I was looking to start working on my board this weekend, but with the bacteria, I just don't see it happening. I have time until my project is due, I just wanted everything done early honestly. Any tips or explaining what I'm doing wrong would be greatly appreciated.

[SciB]

Hi Dcosse,

Sorry to hear your bacterial cultures are not growing as they should. They do take time to form visible colonies, especially at cooler temperatures, so I would give the plates a few more days. If you have a magnifying glass, take a look at the surface of the agar and see if there are any tiny colonies of bacteria or fungi growing.

What kind of agar are you using? Technically agar is JUST the support for the growth of microorganisms. Nutrients have to be added to agar for bacteria to feed on and grow. A commonly used prepared medium sold by scientific supply companies such as Carolina Biologicals is called 'nutrient agar' and it contains glucose, yeast extract, a tryptic protein digest and various salts. I am assuming that when you said agar you meant NUTRIENT agar because plain agar by itself would not support growth of microbes. Be sure to read this information about working with agar if you haven't yet: https://www.sciencebuddies.org/science- ... Agar.shtml

Here's some information about making a light bulb incubator for your plates:

"Place each Petri dish inside a zip lock bag to prevent drying out and to control odors. Turn the plates upside down and put them in a warm place. For many microorganisms, the ideal temperature for incubation is 32°C or 90°F. Bacterial growth should start to become visible in 2-3 days."

"For those growing bacteria at home (for example, investigating bacteria growth at various places around the house), you may use a homemade 'light bulb incubator' in place of a laboratory incubator. This page describes how to construct a "light bulb incubator:" http://www.umsl.edu/~microbes/pdf/Incubator.pdf

Let your plates incubate longer and keep them warm and if you used nutrient or LB agar plates, you will definitely get colonies growing on the surface. Remember to take pictures as they grow for your records and be careful in handling and disposing of the agar because there are a few organisms that can grow under these conditions that could be harmful.

Good luck and keep posting to this thread if you have more questions.

Best wishes,

Sybee

[deleted-132180]

Hey there,

I'm sorry to hear that you still haven't seen bacteria growing on your plates yet, but SciB gave you some excellent advice about other things you can try. One other thing I thought about was how thickly you poured your agar plates. Sometimes, if you pour your plates a little too thinly, the agar will dry out really quickly and the bacteria can't grow very well on them. Make sure that your agar plates aren't drying out! Another thing is, like SciB mentioned, bacteria tend to grow a little slower at cooler temperatures and so it make take a little longer than two days for your colonies to show up. At what temperature are you incubating your plates?

Please feel free to post back with more questions if you need anymore help!

Good luck,
Connie