Due to the interdisciplinary nature of real-world science problems, science education calls for approaches that focus on making connections and allowing students to apply what they learn to meaningful situations (Nagle 2013). To help provide an example of an interdisciplinary real-world biology problem, we have designed a microbiology lesson you can use or modify to fit different focus areas. This lesson incorporates investigation and mathematical representations to examine ecosystem group behavior in the context of cause and effect to population growth or decline. In the lesson, students answer this driving question: Were methods of dealing with microbes used by ancient civilizations effective? Using an inquiry-based lesson and incorporating the Next Generation Science Standards (NGSS) under Ecosystems: Interactions, Energy, and Dynamics (Table 1; see Online Connections), this lesson targets 11th and 12th graders beginning at the intermediate level and uses about five 50-minute class periods. Note that culturing and use of live bacteria or other microorganisms is not recommended at elementary or middle schools and introductory level high school science courses, given the potential biological hazards and health risks.

To start the lesson, share the video “How We Discovered Germs” (see Online Connections). Encourage students to think about the importance of the discovery of microbes and the variety of discoveries as they watch. Following the video, use the World Population History interactive map to show students how human populations increased after the significant microbiology time points mentioned in the video (e.g., pasteurization [1862] and malaria [1880]). Ask students if they think older cultures combatted bacteria and, if so, how? Present them with the following scenario: “You are a worker in ancient Egypt. You were taught that drinking water from the nearby Nile River can make you sick. You, like many others, collect water regularly from the Nile and leave it sitting in copper vessels before using it like you were taught.”

Then task students with the think-pair-share activity in response to the following questions:

• Could copper actually kill bacteria?
• If so, would that have an effect on populations similar to what was seen with the other microbe discoveries?
• What would you need to provide as evidence of copper’s ability to kill bacteria?
• What would you do with the data you collect?

With the class, you can then discuss multiple methods in which scientists can conduct science, potentially drawing from some of the examples presented in the “How We Discovered Germs” video. For example, you might share the story behind some of the discoveries mentioned in the video, such as Louis Pasteur’s discovery of attenuated viruses, Patrick Manson’s discovery that insects can carry parasites, and Robert Koch’s discovery of the cause of anthrax (see Online Connections).

Days 2–4: Collect, analyze, and interpret data

Note: NSTA does not recommend culturing and use of live bacteria at the elementary/middle school level and introductory level high school science courses

For days 2–4, students will explore the answers to these questions by testing copper’s effectiveness as an antimicrobial with an experiment using Escherichia coli (E. coli). Table 2 describes materials needed for this lab. Student and instructor handouts are also available in the supplementary materials (see Online Connections).

In preparation for the second day, you should acquire E. coli cultures (only classic strains of K-12, 1776, B, and C) from a source such as Home Science Tools, New England Biolabs, or American Type Culture Collection. From these stock cultures, you should create cultures for student use by inoculating 3 ml of LB broth with E. coli and incubating the cultures overnight in an incubator set at 37°C. As you do so, it is important to take all proper safety precautions. These include washing your hands with soap and water immediately after completing all lab activities (setup, hands-on, and takedown), then using hand sanitizer. You must also wear indirectly vented chemical splash goggles, a nonlatex apron, and nitrile gloves.

If you do not know how to create these cultures, we suggest you consult the instructor handout in the supplementary materials. Additionally, you should prepare petri dishes with LB agar by dissolving 15 g of bacto agar in 1.0 L of LB medium and sterilizing it by autoclaving. E. coli is a BSL-1 agent. You should ensure that all laboratory space includes a nonporous floor, bench tops, chairs, and stools; a sink with soap for hand washing; an eyewash station; and a lockable door to the room. We also recommend that you keep all personal belongings (including cell phones) in an area separate from the work area.

To begin the lesson on the second day, spend 25–30 minutes introducing and discussing how bacteria grow with the students. It is important to highlight that bacteria multiply rapidly. One suggested way to emphasize that is by doing a small activity with students where they calculate how quickly one bacterium can become 100,000 bacteria. A 15-second video of bacteria growth can provide a good visual aid (see Online Connections). As part of this discussion, you should also return to the experiment ideas students developed on Day 1 and briefly describe the data that they will collect over the next three days. It is important to highlight the bacteria counts present in water before and after being incubated and, as a class, outline how the data can answer the overarching questions.

Divide students into groups of three, and give them the materials necessary to begin their experiment (see Table 2). Base your group assignments on your knowledge of the students—we suggest ensuring that at least one student with strong lab skills is in every group. If classes are small and all students have strong lab skills, students can do the experiment individually. You may also choose to differentiate by putting students in more homogeneous skill groups so they can work to improve those skills.

Groups should distribute 2 L of tap water into two 473 ml copper mugs and one 1 L sample bottles. They should add 0.5 ml of bacterial culture to the water in each container. When handling bacteria cultures or resulting materials (the vessels containing inoculated water or petri dishes), students should wash their hands with soap and water immediately after completing all lab activities (setup, hands-on, and takedown). They must secure loose clothing, wear closed-toe shoes, and tie back long hair. They must wear indirectly vented chemical splash goggles, a nonlatex apron, and nitrile gloves during the setup, hands-on, and takedown segments of the activity. Students must clean and sanitize or disinfect all work area surfaces, materials, equipment, etc. at the completion of the lab activity. You must directly supervise the students during all aspects of lab activities to make sure they are following safety behaviors. More safety standards for working with microorganisms are available on the NSTA website (see Online Connections).

Students should gently dip a sterile dry cotton swab into each vessel. Using a bacteria-damp cotton swab, students should inoculate their plates using a zigzag motion. The students should then properly label their petri dishes to indicate the group initials, date, and vessel they are associated with, tape the petri dishes closed with masking tape, and return the plates to you for incubation. You should store the plates overnight in an incubator set at 37°C while leaving the vessels at room temperature. When finished with cotton swabs, students should place them in dedicated waste containers. These containers can be small kitchen bags separate from regular trash. If accessible, waste should be autoclaved. When removing gloves, students should avoid letting the gloves snap or allowing the outside surface of the gloves to come in contact with their skin.

To begin the lesson on the third day, spend approximately 20 minutes discussing the methods scientists can use to count or isolate bacteria groups. You can aid this discussion by showing the video “Micro Lesson 2: Microbial Growth and Control,” specifically minutes 4:03 through 9:46 (see Online Connections). After this, return the vessels and plates to each group, so they can repeat the steps they took on the previous day. They should gently dip a sterile dry cotton swab into each vessel. Using a bacteria-damp cotton swab, students should inoculate their plates using a zigzag motion. The students should then properly label their petri dishes to indicate the group initials, date, and vessel they are associated with, tape the petri dishes closed with masking tape, and return the plates to you for incubation. As previously mentioned, when handling the vessels containing inoculated water or petri dishes, students should wash their hands with soap and water immediately after completing all lab activities (setup, hands-on, and takedown) and wear indirectly vented chemical splash goggles, a nonlatex apron, and nitrile gloves during all segments of the activity. They should dispose of contaminated swabs and plates in dedicated bags and containers. If accessible, they should be autoclaved. They should dispose of water from vessels by pouring it into a container of bleach solution at approximately 118 ml bleach per 4 L water.

On the fourth day, groups can count the number of colonies on the incubated plates. Students should count each colony dot once. They can use markers to mark the colonies already counted on the petri dishes. After counting, students should return plates to you for proper disposal (we recommend sterilizing plates using an autoclave). Using the data collected from counting colonies, students should prepare graphs showing the number of colonies for each vessel using Microsoft Excel (or another graphing software such as Google Sheets). This may be another point where you could choose to differentiate. Depending on your student skill level, students could make bar graphs, pie charts, or line graphs. You may also see that some students need more support than others, so determining if you want each student to do it on their own or work as a group is another choice you may make to differentiate instruction.

You should guide students in inputting their data into Microsoft Excel or Google Sheets and creating a graph if they are not familiar with these skills. You should then discuss general trends of the results with the students. We also suggest collecting whole-class data and making a summary graph. Use this to guide discussion of trends and the potential effect and significant effects on populations, using the map and timeline on the main page of World Population History and discussing similar public health milestones (e.g., the introduction of antibiotics [1940], antiseptic procedures [1847]).

Day 5: Assessment

To conclude the lesson, assess student learning by tasking students with using their data and graphs from the previous day and creating a claim-evidence-reasoning (CER) explanation (template is provided in the supplementary materials) about the study and how the results may relate to human population dynamics. To guide their thinking, give students the following questions: How did this finding likely affect these ancient populations? How would they be without it? How would communities with and without access to copper differ?

We allowed students the entire class period to complete their CER. The CER acts as a summative assessment that provides evidence of the student’s ability to use the evidence they collected and make a claim. CERs should be assessed using the rubric in Table 3 (see Online Connections).

Conclusion

Overall, this lesson is effective at giving students an inquiry-based introduction to antimicrobials. The lesson also incorporates social sciences by allowing students to frame their results in relation to human population dynamics. Our students enjoyed the investigation and thinking through how copper can affect bacteria. With advanced students, you can briefly discuss how the free electron in copper’s outer orbital shell prevents cell respiration in bacteria.

Online Connections

Table 1. Connecting to the Next Generation Science Standards (NGSS):

www.nsta.org/sites/default/files/journal-articles/TST90-3/Whitworth/Table_1.docx.

Table 3. Assessment rubric: www.nsta.org/sites/default/files/journal-articles/TST90-3/Whitworth/Table_3_7.27.2022.docx.

Supplementary Materials 1. Ancient Antimicrobials: https://docs.google.com/document/d/1LtrrXKKxX0K7iiX7PNvIy5me1ODwfXeoyR0ocXoK_-I/edit?usp=sharing.

Supplementary Materials 2. Ancient Antimicrobials Experiment Instructor Guide: https://docs.google.com/document/d/1liM50qc9_nvNdg6o-QsIMdIFBvaRKqmShm9CgsVl0Mw/edit?usp=sharing.

Supplementary Materials 3. Ancient Antimicrobials CER Template: https://docs.google.com/document/d/1YTa4tqyZoq8f5WL-F2-3WI68cFtYjPIi0XtsDBOPMwk.

How We Discovered Germs by PBS Digital Studios: www.pbs.org/video/how-we-discovered-germs-ots3wv.

World Population History: https://worldpopulationhistory.org.

Louis Pasteur’s discovery of attenuated viruses: www.sciencehistory.org/historical-profile/louis-pasteur.

Patrick Manson’s discovery that insects can carry parasites: www.jstor.org/stable/4452995?seq=8.

Robert Koch’s discovery of the cause of anthrax: www.newscientist.com/people/robert-koch.

Tips for the Safer Handling of Microorganisms in the Science Laboratory: https://static.nsta.org/pdfs/TipsForSafeHandlingOfMicroorganisms20160412.pdf.

Micro Lesson 2: Microbial Growth and Control: https://youtu.be/8rTkETJZwUU.

Bacteria Growth: https://youtu.be/gEwzDydciWc.

Tips for safer handling microorganisms in the school science laboratory:

http://static.nsta.org/pdfs/TipsForSafeHandlingOfMicroorganisms20160412.pdf.

Akacia Halliday-Isaac is a doctoral student in biology at the University of Mississippi, University Park, MS. Brooke A. Whitworth (bwhitwo@clemson.edu) is an associate professor of Science Education and the Teaching and Learning Ph.D. Program Coordinator, Clemson University, Clemson, SC.