Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Growing and killing bacteria
Name: Jennifer A Buckner
Age: N/A
Location: N/A
Country: N/A
Date: N/A 

I am in the ninth grade. I want to do a project on effective ways to kill bacteria. I am looking for ways to grow bacteria and to tell how much bacteria has been killed. Can anyone help me with a way to do this experiment and do repeated test.
Thank You for your help.

The easiest way would be to determine the number of living bacteria present before and after treatment. You can do this by spreading a small volume of a cell suspension on a nutrient agar surface in a petri plate. After incubation for a day or two, you should see a number of colonies. Each colony corresponds to a single living cell present in the original suspension. Counting the colonies therefore gives you the number of cells living cells present at the time of plating. You could compare the numbers for treated and control samples to see how effective the killing treatment was. Keep in mind that a confluent plate (with all colonies run together) or a plate with no colonies will not give you any information about the number of living cells. Therefore, it is necessary to plate a number of dilutions for each sample. Then, at least one or two plates will contain an appropriate number of cells for counting (usually 30-300 colonies is a good number). All of this assumes that you have access to some basic tools of microbiology. If your school does not have the necessary equipment (autoclave, nutrient media, etc.), contact someone at a local college. Often, these people are willing to assist high school students in these projects.

Brian Schwartz

Click here to return to the Biology Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (, or at Argonne's Educational Programs

Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory