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Kitchen Lab

Homemade Agar Plates

 

  • ½ teaspoon of beef/vegetable or chicken stock powder

  • ¼ cup of water

  • 1 teaspoon of sugar

  • 1 teaspoon of gelatin

  • Saucepan for boiling mixture

  • 2 x sealable containers

  • Spoon

  • Sticky tape

  • Writing tool

  • Cotton swab (optional)

  • Warm area

YOU NEED:

WHAT TO DO:

  1. Pour the water into the saucepan and bring to the boil. Add beef stock powder, sugar and gelatin to the boiling water and stir for a minute until all the ingredients have dissolved. Cool your new agar mixture slightly for 10 minutes. The mixture needs to be still hot to avoid the gelatin setting in the saucepan and to prevent contamination from bacteria in the air. The conditions are far from sterile, but you want to avoid as much contamination as possible.

  2. Take the lid off the Petri dishes and half-fill the petri dish with the hot mixture. Only take the lid off the petri dish when you are ready to pour your agar, or they will become contaminated with the bacteria in the air.
    Immediately put the lid back on the Petri dish and put it in the fridge for about 4 hours until the agar has set.      

    Do not touch the agar.

  3. Now it’s time to collect and grow your bacteria on the agar plates. Bacteria is not hard to collect because it is everywhere. Try exposing one plate to the air in your house, dorm, or apartment and using a cotton swab run it along the inside of your mouth, nose, hands, feet, belly button, door handle, phone, or computer (Pick only 1 option. It does not have to be from the examples previously listed.) And then slightly run it across the agar in a zig zag motion.

  4. Put the lids back on the Petri dishes, label them, tape them closed and place them upside down in your make-do incubator (if you have one) for 1 to 2 days. If you don’t have an incubator, leave the plates at room temperature for 3-5 days. Out of precaution do not open your sealed Petri dishes.

  5. Observe your results and take pictures of your plates. Write a brief summary of your findings. Describe the shape, color, and texture of the bacteria in your plate, include what area you swabbed for microbes, and research the relevant microbes found in that area. For example, if you swabbed your hands research typical bacteria found on hands. Include these findings in your brief summary for submission.

     

     

     

     

     

     

     

     

     

I began the experiment on Tuesday, January 19, with the creation of my agar. I followed the directions of what to buy at the grocery store and got to work!

I poured the agar into two sealable containers and then refrigerated them for four hours. I opened one of the containers to the air inside my apartment, and the other I scraped with a cotton swab of my mouth saliva. I proceeded to leave them under a lamp for the next five days.

 AIR BACTERIA 

 MOUTH BACTERIA 

Unfortunately, after five days of sitting, it wasn't exactly clear if anything had occurred. The agar that had solely been exposed to the air was clearly unaffected. The agar that had been scraped with the cotton swab looked as if it had been eaten through yet there was no visible growth.

 

What went wrong?

 

I think that overall it was too cold in my apartment to make it a suitable growing environment for bacteria. However, it was very frustrating to have empty agar plates after a week of waiting; especially while all along I thought that I was culturing an exciting project!

Identifying Bacteria

Although there was no noticeable growth in my agar plates, I still researched what types of bacteria would grow from a swab of my mouth, had the experiment been successful. Click on the aqua and pink buttons to find out more about the microbiology of the oral cavity!

 

From the National Center of Biotechnology Information, I discovered that the normal bacterial flora of the oral cavity mostly belong to the genera of Gemella, Granulicatella, Streptococcus, and Veillonella. Because of the wide range of surfaces within the mouth, the species of bacteria are very diverse and can be completely harmless or pathogenic. 

 

 

 

 

From another scientific source, I found that from the area that I swabbed (my cheek), the bacteria would predominantly be that of the genus Streptococcus. 

 

 

 

 

 

From here I will focus on the different species of Streptococcus bacteria that can be found within the oral cavity. These bacteria make up nearly 20% of the oral microflora. One example is the Streptococcus mutans. These bacteria are gram-positive bacteria with a coccus shape. They are predominantly known for their involvement of human tooth decay. It colonizes itself in human hosts and is very easily transmitted between humans that come in contact, considering it is still part of the normal flora of the oral cavity despite its infectious nature. 

 

 

 

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