Re: how do i test spices impact on bacterial growth?

Hi Nathan -

To test spices mixed with the agar you would probably want to do a tube dilution test. A tube dilution test is used to establish the minimum inhibitor concentration of a particular agent. In this case it would be the spices. The test would consist of a series of test tubes containing:

• Different concentrations of the spices you wish to test along
• Growth media which would be in the form of a broth.
• Your bacteria.

Once you have them mixed the tubes should be placed in an incubator for 24 to 48 hours at a temperature of 35.0 celcius. This allows for optimal growth for most bacteria. Depending on your available resources, if you do not have a incubator place the tubes in a room that stays at a fairly consistant temperature and record the temperature. After the incubation time any growth in the tubes will be indicated by a cloudy appearance, and the more cloudy they appear the higher the bacterial growth. The clearer they appear the less growth has occurred. Clear tubes indicate no growth has occurred and this concentration would establish the minimum inhibitor concentration of that particular spice.

You could then take the test tube that show growth and swab them and put them on agar dishes and incubate for the same amount of time and temperature and do a total plate count along with the tube containing no spices. This would allow you to determine how effective the spices are at different concentration.

As far as the agar and broth, unless you are testing for a specific type of bacteria then standard "rich media" agar plates or broth will work for most bacteria. The bacteria can be grown from a sample culture. If you do not have any sample cultures at your school check with your teacher to see if he or she could order it along with the agar and broth. Most scientific catalogs will have bacteria cultures and agar the prices will vary depending on what type of agar and culture you are looking for. If you are unable to do this then if you have any colleges around your area check with them because they will most likely have these items on hand and would probably glad to help you.

As far as the need for a microscope, you should not unless you want to see individual bacteria. Bacterial growth on a dish will appear as tiny spheres or dots. These dots represent colonies of bacteria and the dots are what you count for your total plate count.

You have selected a excellent project to do in fact the researchers at Kansas State University are doing research on spices and their ability to reduce bacteria such as the deadly E. coli 0157 H strain. I read this from the Meat and Poultry web site at:

http://www.meatpoultry.com/archives98/oct98/1098-9.htm

If you need help with laboratory proceedures you may get help from the web by typing in microbiology lab technics in your search engine. Good luck on your project and if you have any more questions please do not hesitate to ask. Thanks for asking and I hope this helps you.

Thanks Larry