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Name: Markita
Status: Student
Grade:  6-8
Location: MI
Country: United States
Date: December 2005


Question:
I am in the eighth grade. I want to to do a science fair project on killng bacteria. My project is me trying to see if household seasonings such as season salt can killed bacteria. I want to know how to find out how much bacteria has been killed each day and how to run the trials successfully? And one more thing, do you think this is a good idea?



Replies:
I think these bacterial inhibition experiments are OK as long as they are use an innocuous strain of *E. coli.* These strains can be obtained from the ATCC (American Type Culture Collection) or from biological supply houses like Carolina Biological Supply. Specifically, the seasoned salt experiment would not reveal much because salt alone would inhibit virtually all bacterial growth. Dropping a few grains of a seasoning on a plate seeded with approximately 10^6 bacteria, should show a zone of inhibition around the seasoning if it does inhibit growth.

Ron Baker, Ph.D.


] I can think of a lot of reasons NOT to attempt such experiments:

For starters:

1. Safety/Supervision.
2. Control setups (temperature, nutrients, etc.).
3. Defined objective(s).
4. Equipment/measurement/experimental methods.

A particular school might have a staff member that can address these (and other) issues, but that is the exception, not the rule. I don't think you have to be a PhD in chemistry to recommend NOT doing experiments with mercury, elemental phosphorous and any number of other chemical substances. Any proposal for a science fair project should be able to provide definite answers to the above reasons before beginning any such project.

Vince Calder Ph.D.


I think that this is a great idea but I'm a little worried about you doing it at home. It depends what type of bacteria you will be using. If you are using bacteria you collected yourself, it could be dangerous because you don't know exactly what you are working with. If you order it from a biological supply company, order something like Bacillus megaterium that is not known to make people sick. I also think you should work under the guidance of a teacher because it is very easy to contaminate your work if you aren't super careful.

As far as the experiment is concerned, you should do serial dilutions of your bacteria until you find a plate that has a number of bacteria you can count.

You can google "serial dilutions + bacteria" and probably find directions how to do this, or look in any microbiology lab manual. This way, you can actually count the bacteria and determine if the concentration of your spice, etc. has an effect on them. I would also familiarize myself with the rules of aseptic technique (you can also google this) that will tell how to work with bacteria safely and also to keep from contaminating your work with other bacteria.

Good luck

vanhoeck



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