Science Buddies: "Ask an Expert"

Hi,
I need to conduct an interview for my science fair experiment. I am testing the 5 second rule, checking to see how much bacteria the food will collect after being "contaminated" for 5 seconds. I am using cooked chicken, bread and a hard candy. We are using the kitchen floor, and the driveway outside.

I have some questions about how to get my samples in the petri dishes. Can I just rub the piece of chicken directly on the petri dish? Or should I use a sterile swab to wipe the surface of the dropped chicken, then rub that on the petri dish? Do you suggest that I swab one petri dish with nothing on it, to show that the dishes were uncontimated to begin with?


Should the swabs be wet or dry? I wonder about this since if someone were to go ahead and eat the food, it would go into their digestive system which is "moist" (vs. dry).



Here are my interview questions:
1. If there is bacteria on the food that is dropped, will it still grow if I decide to eat it right away?

2. DO you think that the bacteia will grow into mold in the petri dishes?

3. About how long (do you think) will it take for the bacteria to grow?

4. Would I need to use a microscope to see the bacteria?

5. What are the most common types of bacteria found on a floor?

6. How can you identify the different types of bacteria found?

7. Why would the bacteria be so harmful if it has barely had time to touch the ground before it's eaten?

8. Without a microscope would we be able to identify the different types of bacteria?

Thankyou for your time and answers. i'm sure i'll be posting more questions throughout my experiament
(these are my smilies =0=0=0=0=0)

Hi Laurie,

There are many questions here and I'll try to answer as many as I can.

A sterile swab is a good idea and you can use it dry. It's always a good idea to have a "control plate" that has only been touched by a clean swab to show that your swabs are indeed sterile and perhaps another plate that has not been swabbed to show that the plates are clean.

1. Bacteria are everywhere. The ones we need to worry about are the those that can cause disease. You ingest bacteria everyday and you body can handle almost everything you eat. Think about your stomach and what kind of environment that is like.

2. Bacteria will not turn into mold as they are different organisms but you may also get mold growth on your plates.

3. In a warm environment (not hot, body temperature or even a bit lower is fine) you should see visible colonies in a day or two. You may see more as time goes by. Keep the plates closed.

4. You will not need a microscope to see the colonies but if you want to look at the individual cells you would.

5. Hard to say.

6. There are many techniques to identify and classify bacteria. Through microscopy you can see what the shape of the bacteria are and using special stains you can further identify categories of organisms. There are also genetic techniques available to identify what organism you have.

7. This isn't always the case. You eat foods that grow in the ground like carrots without harm. It isn't the soil that's the issue it's the type of organism that you need to be concerned about. Certain bacteria are harmful and they tend to be found under certain conditions like contaminated water sources. Perhaps you should look into some organisms like Salmonella enterica to see what I am referring to.

8. You could if you had access to genetic tools which I don't expect you do.

I hope you find this helpful. Good luck

Holly