Science Buddies: "Ask an Expert"

Hello, I'm going to have a science fair this year. My topic is to observe which plant extracts affect the death of bacteria the most. I've completed the procedure of my experiment by asking lots of experts, but I'm not sure about safety, so I want to get a final check from experts.
I'm going to do this experiment at home. I will disinfect all items and place before and after the experiment.
First of all, I'm going to put the E. coli culture solution in one of the six petri dishes, and the other five petri dishes are going to put the culture solution with 5 different types of plant extracts. Is it okay to add plant extract and culture solution together at the same time? Because, while culturing E. coli in a petri dish, I tried to open the lid of a petri dish and add the extract, but it could make me infected. Will I be able to get definite result even though I do this? Also, since I can't get a professional machine, is there a way to store and seal petri dishes so that they don't get contaminated from other bacteria as much as possible? If there's a safety rule that I must follow, I'd appreciate it if you could tell me more.

Thank you and have a nice day

Hello!

Are you using the K-12 strain of E. coli? That strain is not harmful to humans, so it's quite safe to use. As you mentioned, just make sure to disinfect your workspace after you finish the experiment and wash your hands after working with the bacteria. Also make sure to wear gloves while working with the bacteria to prevent any from getting on your skin and to prevent any microorganisms from your skin from contaminating your bacterial cultures.

The bacteria in the petri dishes are unlikely to spread to you when you open the dishes to add the extracts. To avoid contaminating the plates when you add the extracts, open the lid of the petri dish just wide enough to get the extracts inside but don't remove the lid of the petri dish completely. That could allow other bacteria and fungi to get onto your plates and contaminate them. To seal your plates, you can wrap Parafilm around the perimeter of the plate to seal it and then wrap the whole plate in cling wrap. You can refrigerate the plates to make them last longer without getting moldy.

Please let us know if you have any more questions!