INTRODUCTION / BACKGROUND

This case study was designed for the seminar component of Introductory Biology at Duke University. In addition to seminar, students in this course also attend lecture and laboratory. Teaching assistant (TA) mentors lead the 12-student seminars during which students engage in directed inquiry exercises. Students work through the case study in the second week of the course. Topics covered in the lecture and lab components of the course prior to this case include organisms and cells as units of life, proteins and membranes, DNA structure, replication, and repair, and how to ask good questions in biology.

Objectives

After completing this case, students should be able to:

1. Describe some of the biochemical mechanisms by which antibiotics act against bacteria.
2. Evaluate which antibiotics would be effective against a given type of bacteria.
3. Apply their basic knowledge of DNA, genes, and proteins (and the relationship between them) to a new question. That is, how do changes in DNA observed by pulsed-field gel electorophoresis impact patterns of antibiotic resistance?
4. Synthesize the relationship between antibiotic consumption and antibiotic resistance based on what they have learned about bacteria, antibiotics, and natural selection.
5. More adeptly use data from charts and gels to answer questions.

CLASSROOM MANAGEMENT

Students are expected to have read the background information about bacteria, antibiotics, and the evolution of antibiotic resistance before coming to class. We assigned this reading in seminar the previous week. The primary aim of the reading is to introduce students to the topics of bacteria, antibiotics and antibiotic resistance.

This case is designed as an "interrupted case," that is, students are given one piece of information at a time and asked to do something with that information. After they have completed one part, they receive the next piece of information. There are four parts to the exercise.

Given that we use this case study for our 12-student seminar sections, we make the following suggestions to TA mentors about how to teach the case although they are free to choose whichever method they think will work best with their particular section.

1. Small group work. Each group of three or four students receives the first part of the exercise and is given a specified amount of time to work through the questions in that part. At the end of the designated time, the TA mentor surveys most or all of the groups for their answers, then hands out the next part. Again, groups are given a specified amount of time to work through the problem and are surveyed by the TA mentor about their answers. The exercise is written so that the TA mentor needs to provide little information during the polling times; each new part provides "the answer" to the previous part. However, this changes after Part IV when students are asked three questions that challenge them to think about how antibiotics select for resistant strains and the molecular events that lead to the emergence of a new strain of bacteria. Part IV offers a lead-in for TA mentors to end seminar with a class-wide discussion about these more open-ended questions.

2. NOTE: Our TA mentors have found that assigning specific jobs (e.g., group leader; time keeper, and recorder/reporter) to each student in a group helps to keep group work moving at a steady pace.

3. Class-wide discussion. In this format, the TA mentor functions as the group leader and moves students as a class through the exercise. The TA mentor hands out each part, gives students a chance to read the information, then begins discussing the problem. This format allows the TA mentor to exert more control over the classroom, but may prevent some of the quieter students from becoming as involved in the discussion.

In terms of time requirements, in Introductory Biology, seminar lasts 50 minutes. Based on TA mentors' experiences, we estimate only five to seven minutes for both Parts I and II since they are rather straightforward. Part III is generally the most challenging part, and Part IV generates the most interesting discussion. Because of this, we recommend allowing at least 15 minutes for each of these parts. It might also be possible to expand this case study beyond a 50-minute class session so that there would be time for more discussion among students and between students and the instructor during each part of the exercise. Although the current constraints of Introductory Biology at Duke University prevent us from taking this approach, individuals who use this case study should feel free to make such adaptations.

ANSWER KEY

Answers to the questions posed in the case study are provided in a separate answer key to the case.  Those answers are password-protected.  To access the answers for this case, go to the key.  You will be prompted for a username and password.  If you have not yet registered with us, you can see whether you are eligible for an account by reviewing our password policy and then apply online.

ASSESSMENT OF LEARNING GOALS

As explained in the background reading, we use this case in Introductory Biology as one of three installments in a series on antibiotic resistance. After working through this case, students deal with the topic again in lab by surveying for the prevalence of antibiotic resistant bacteria carried by them and their peers and in nearby water supplies (Lemons et al.). Finally, students work in groups during seminar and outside of seminar to collect their results from lab and analyze these results via a writing assignment.

Due to this structure, we do not use the case study class period for assessment. Rather, we assess whether they have achieved the specified learning objectives in three independent ways. First, in the lab that follows this case, students design an experiment in which they select antibiotics that will be effective against members of the genus Staphylococcus and members of the family Enterobacteriaceae. Thus, TA mentors are able to assess how well students are achieving learning objective 2 as they observe the quality of each student's experimental setup. Second, students are assessed by their performance on a group writing assignment dealing with antibiotic resistance. As part of this assignment, students must synthesize what they have learned from lab about the relationship between antibiotic resistance and antibiotic consumption (learning objective 4) to address the concern that Dr. Collins raises in Week 2, Day 10 of the case (i.e., that increased use of antibiotics will lead to the emergence of new strains of resistant bacteria). Finally, on exams, students are responsible for concepts that have been covered not only in lecture but also in lab and seminar. Therefore, we frequently use the curriculum on antibiotic resistance as a source for exam questions.

ADDITIONAL COMMENTS AND RECOMMENDATIONS

• Many of our TA mentors report that students are highly engaged by and become emotionally invested in the case. For example, they express frustration that Dr. Collins did not prescribe the antibiotic that they recommended and feel that the outcome for Kayla Starnes would have been different if she had.
• Some TA mentors caution that due to the large amount of reading involved in the case, managing individual students and groups of students who read at different paces can be challenging. Perhaps one solution is to predetermine groups such that differences in pace among individual students and groups of students will be minimized. Some TA mentors have also found it helpful to have a series of additional questions for each part prepared ahead of time for groups that work more quickly than others.
• In response to TA mentors comments, Part III was rearranged to place the description of pulsed-field gel electrophoresis into an appendix-like subsection. While some TA mentors felt that it was worthwhile for students to invest time in understanding this technique, others felt that it was not essential. We hope that including it as a subsection to Part III gives you the leeway to either use or ignore this portion of the exercise.

FOLLOW-UP WRITING ASSIGNMENT

The students are given the following assignment in connection with this case study:

REFERENCES

Acknowledgements: This case study was developed with support from The Pew Charitable Trusts and the National Science Foundation as part of the Case Studies in Science Workshop held at the State University of New York at Buffalo on May 22-26, 2000.

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