Bacteria Not Growing

[deleted-510833]

I am doing an experiment how temperature and light affect bacteria growth. My bacteria source was from my mouth. I did 8 agar plates placing 4 in a heated environment and 4 in a cool environment, 2 plates in each environment are in source of light and 2 are in darkness. Only 1 plate out of the 8 yielded bacteria growth. Can you suggest another source of bacteria for my retrial?

Thanks.

[sunmoonstars]

HI,

The microbes in your mouth are of many different species. You could try your experiment again, or try to get a pure culture from Carolina Scientific or NEB - both sell K12 E. coli strains for research use.

Also, make sure you are familiar with the safety guide:

https://www.sciencebuddies.org/science- ... fety.shtml

Let me know if you have further questions. I hope you enjoyed your project, even if the results are confusing.

Tonya

[deleted-132180]

Hello there,

That is a very interesting experiment and result. Just out of curiosity, which condition out of the eight actually yielded bacterial growth? How hot is the heated environment, and how are you providing the heat source? How cold is the cool environment? What is the light source that you're using?

As the previous expert mentioned, there are lots of different bacterial species in your mouth. Hence, it is very possible that many of those species required special conditions to grow and may not be able to grow in the conditions that you used. Because there are different bacterial species from your mouth, it'll also be difficult to assess how each of your conditions affected the growth of each individual species. Also, are you swabbing your mouth eight times, and streaking each individual swab onto a different plate each time? It's also possible that you obtain different amounts of bacteria each time you swab your mouth, and that is another variable that will make it hard to compare the growth in each of your conditions. For example, you may see lots of growth on one plate compared to another, but it could just be the fact that you happened to swab more bacteria from your mouth onto that particular plate, and not necessarily because of the growth condition.

I like the previous expert's suggestion about purchasing a pure culture of one bacterial species such as K12 E. coli and see how your different conditions affect specifically how E. coli grow. With this approach, you're able to make sure that you plate the same number of E. coli onto each of your eight agar plates, and see whether certain conditions allow the bacteria to grow better than other conditions.

Let us know if you have any other questions!

Connie