Trouble growing bacteria in petri dishes
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Trouble growing bacteria in petri dishes
I am growing unknown bacteria that i collected from my house floor for my science fair experiment. I'm testing whether the five second rule is real. I ordered a petri dish kit with nutrient agar, sterile swabs for collecting the bacteria, and sterile plates. I put them in the darkest place in my house which is approximately 70 degrees F to grow. It's been more than 48 hours but I'm not seeing anything on the surface of the petri dishes. I need to finish this experiment and turn in my results very soon. What am i doing wrong? Should i redo my experiment? Please help!!!
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jskanderson
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Re: Trouble growing bacteria in petri dishes
Hi Aalee,aalee wrote:I am growing unknown bacteria that i collected from my house floor for my science fair experiment. I'm testing whether the five second rule is real. I ordered a petri dish kit with nutrient agar, sterile swabs for collecting the bacteria, and sterile plates. I put them in the darkest place in my house which is approximately 70 degrees F to grow. It's been more than 48 hours but I'm not seeing anything on the surface of the petri dishes. I need to finish this experiment and turn in my results very soon. What am i doing wrong? Should i redo my experiment? Please help!!!
If the petri dishes came pre-made in the kit, then the cause of the lack of bacterial growth might be due to temperature. There is a likely chance that 70 degrees Fahrenheit won't be warm enough to culture the bacteria, so I would suggest redoing the data collection (swabbing the floor for bacteria and streaking onto the petri dishes) and placing the petri dishes in a dark place that's at least 75-85 degrees Fahrenheit.
Perhaps this video will help: https://www.youtube.com/watch?v=A0b6_kg2oMc
Hope this helped!
-JSK
~ Call me JSK 
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Re: Trouble growing bacteria in petri dishes
Hello, JSK
Thank you so much for your reply! was just wondering, should I order a new petri dish kit online or reuse the pertri dishes that I already have and sterilize them again? And also, I am using snack crackers that have a small amount of salt on the surface to drop on the floor, pick up after 5 seconds, and swab for data. My father told me that the salt could kill the bacteria, and that I should use plain bread instead. Is my father correct?
Thank you so much for your reply! was just wondering, should I order a new petri dish kit online or reuse the pertri dishes that I already have and sterilize them again? And also, I am using snack crackers that have a small amount of salt on the surface to drop on the floor, pick up after 5 seconds, and swab for data. My father told me that the salt could kill the bacteria, and that I should use plain bread instead. Is my father correct?
Re: Trouble growing bacteria in petri dishes
Hi Aalee,
If you are using a reusable type of petri dishes (the glass ones), you can go ahead and sterilize them (by placing them in boiling water for at least 15 minutes, then carefully removing them with tongs and placing them on a clean surface to cool) and reuse them. However, if you used the disposable plastic ones, I would recommend ordering a new kit since most methods to sterilize plastic dishes won't kill all the bacteria.
Your father is correct about the salt: salt is attracted to and absorbs water. This means that it can suck the water out of cells, causing them to die. I would use a piece of plain bread for your experiment.
Hope this helped,
Allison
If you are using a reusable type of petri dishes (the glass ones), you can go ahead and sterilize them (by placing them in boiling water for at least 15 minutes, then carefully removing them with tongs and placing them on a clean surface to cool) and reuse them. However, if you used the disposable plastic ones, I would recommend ordering a new kit since most methods to sterilize plastic dishes won't kill all the bacteria.
Your father is correct about the salt: salt is attracted to and absorbs water. This means that it can suck the water out of cells, causing them to die. I would use a piece of plain bread for your experiment.
Hope this helped,
Allison
Re: Trouble growing bacteria in petri dishes
Hi Aalee,
Bacterial growth at room temperature is pretty slow. If you don't have access to an incubator or something like it, you'll want to wait a week or so before writing off the plates as failures.
Just to be safe, though, you should consider leaving one plate without any swabbing as a negative control
-EG
Bacterial growth at room temperature is pretty slow. If you don't have access to an incubator or something like it, you'll want to wait a week or so before writing off the plates as failures.
Just to be safe, though, you should consider leaving one plate without any swabbing as a negative control
-EG