Maximizing STEM learning in microbiology laboratory through bacterial enumeration

• In Event: Science Education Oral Session 1

Abstract

An important concept that biology students often struggle with is serial dilution. This concept combines mathematics and logic, and when taught in a microbiology laboratory, generates an attainable STEM-based learning environment. I have developed a two-laboratory session lesson in bacterial enumeration techniques that challenges the students through a real-life problem. Furthermore, the lesson helps the students discover the link between direct and indirect methods of determining bacterial concentrations. During the first laboratory session, students learn the basis of various microbial enumeration techniques through inquiry-based teaching that challenges students’ higher order thinking skills. Each group is then given a bacterial broth culture with an unknown concentration of bacteria. Students will set up the serial dilution experiment and plate the bacteria from each of the dilutions on agar plates. Students will also generate a different serial dilution series and measure the turbidity. During the second laboratory session, students identify a plate set with a countable number of colonies on it. Students use these colony counts to determine the bacterial concentration of their unknown. Furthermore, students form a link between the direct and indirect enumeration techniques by generating a standard curve of absorbance versus bacterial concentration. Finally, students are asked to determine a concentration of a bacterial unknown without the use of serial dilution and plate count, but rather using their standard curve ensuring that the link between the direct and indirect methods was mastered. This lesson has contributed to the increase of student section scores in the senior biology laboratory exam.

Author

• Joni H Ylostalo, University of Mary Hardin-Baylor