Serial Dilution: Tracking Bacterial Population Size and Antibiotic Resistance

Anton E. Weisstein, Truman State University, Kirksville, MO
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This material is replicated on a number of sites as part of the SERC Pedagogic Service Project


Serial dilution allows estimation of a range of bacterial population sizes. Percent resistance can be calculated by culturing bacteria on both antibiotic-free and antibiotic-containing media and comparing the results. In this Spreadsheet Across the Curriculum module, students explore the quantitative concepts of ratios and percentages and then apply those concepts to build Excel sheets that calculate bacterial population size and percent resistance.

Learning Goals

Quantitive Goals: Students will develop a deeper and more explicit understanding of proportions, ratios, and populations of inference. They can also review scientific notation if necessary.

Spreadsheet Goals: Students will learn to use simple mathematical formulas in Excel. If they complete the optional appendix, they will also learn how to apply the IF and OR logical functions.

Biology (Content) Goals: Students will be able to calculate bacterial population size and percent resistance based on the number of colonies observed on agar plates after serial dilution.

Context for Use

This module is intended for use in the last few weeks of a majors introductory biology course. Students will work on this module (in their regular lab groups of four) in the lab, immediately after setting up a serial dilution experiment. They should then be able to interpret the results when the colonies have grown a few days later.

Description and Teaching Materials

PowerPoint SSAC2006:QR67.AEW1.1-Student (PowerPoint 807kB Feb15 07)

If the embedded spreadsheets in the PowerPoint module are not visible, save the file to disk and open it from there.

This PowerPoint file is the student version of the module. An instructor version is available by request. The instructor version includes the completed spreadsheet. Send your request to Len Vacher ( by filling out and submitting the Instructor Module Request Form.

Teaching Notes and Tips

I have not used this module in class yet.


The student version of the module includes an end-of-module assignment that can be used for assessment. The instructor version also includes a pre-test that can be coupled with the end-of-module assignment.

References and Resources

Other Excel-based digital classroom resources in biology:
The Biological ESTEEM Collection – a project of the BioQUEST Curriculum Consortium