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Activity 3 - Superbugs: An Evolving Concern

3. Convene a brief class discussion in which you clarify any confusion you noted as you circulated among the groups and/or invite students to ask questions about the results of their experiments.

4. Tell students that they will watch a young woman named Debi French discuss her battle with tuberculosis. Then they will use the results of their bacterial growth experiments to help explain what happened in her struggle with the disease. Instruct teams to take their copies of the flow chart and Discussion Questions with them to the computer stations.

Möbius StripAs they use the results of their bacterial growth experiment to explain what happened to Debi French, students will experience how basic research leads to explanations for disease and for the success or failure of disease treatment. This understanding leads scientists to propose further research and policies directed at improving public health.

Emphasize that the bacterium in their experiment (P. fluorescens) is not the kind that causes tuberculosis (M. tuberculosis). P. fluorescens does not cause disease in healthy people. Furthermore, the antibiotic kanamycin is not used clinically, so the resistant bacteria cultured in this exercise do not compromise medical treatments. Emphasize, however, that all bacterial cultures in your class are decontaminated before disposal and that aseptic conditions must be followed in all work with microorganisms.

5. Distribute a copy of Master 3.3, Debi's Story: Explaining What Happened, to each student and tell them to click on Debi's Story to start the video. Indicate that students have 20 minutes to answer the questions on Debi's Story.

You may want to emphasize to students that this is a true story, and that Debi herself tells her story on the video.

Organizing student teams at individual computer stations to view Debi French's story will allow them to complete this part of the activity at their own pace. An alternative, if you have the equipment to project the video from the Web site onto a large screen for whole-class viewing, is to show the first part of the video to the class, then reorganize students into their teams. After the teams have discussed and written answers to the first set of questions on Debi's Story, reconvene the class to watch the second part of the video. Instruct students to return to their teams to answer the second set of questions on the handout. Follow this process until students have completed their study of Debi's story.

You may need to remind students of the information they learned about tuberculosis in Activity 1.

puzzle pieceThe Debi French example reminds students of the major concept of the activity: One explanation for the re-emergence of infectious diseases is resistance of the causative agent to the treatment that once cured infections of that agent. The important public health issue is avoiding inappropriate use of antibiotics as a way to minimize, or at least delay, the evolution of resistant pathogens.

6. Convene a whole-class discussion in which you ask several teams to share their responses to the questions on Debi's Story. Invite the other teams to add information and disagree with these responses. Then ask students, "What does the Debi French example suggest is an explanation for the re-emergence of diseases like tuberculosis?"

Students should be able to provide answers such as the following:

Question 1

. Debi contracted tuberculosis (TB) from a student in one of her classes who had an active, misdiagnosed case of TB. Debi did not know this student.

. The symptoms Debi had were fatigue, weight loss, and a severe, persistent cough.

Question 2

. The treatment to cure TB is a combination of several antibiotics. Debi named standard drugs used for TB such as isoniazid and streptomycin.

. When Debi started the treatment she initially got better.

Question 3

. Debi's health began improving when she started the drug therapy for TB because the bacteria that caused her tuberculosis were killed (or their growth was inhibited) by the drugs she was taking.

Question 4

. On Valentine's Day 1994, Debi learned that her tuberculosis was active again.

. The drugs Debi took to cure her TB were not working because the bacteria that caused her TB had become resistant to the drugs.

Question 5

. Debi had a relapse (developed an active case of TB again), even though her health had improved and she was still taking the drugs to cure TB, because the initial treatment killed some of the disease-causing bacteria, but those that were resistant survived. They continued to multiply, passing their resistance on to their progeny. As a result, the disease in Debi's lungs returned. But now, the disease-causing bacteria were all resistant to the drugs she was taking and the drugs were no longer able to cure her. Point out to students that this is an example of natural selection: The resistant bacteria survived and passed the genes for resistance on to their progeny, whereas the susceptible bacteria did not survive. Soon all or most of the bacterial population, descendants of the resistant organisms, was resistant.

Question 6

. Debi was finally cured of TB by taking other drugs that were still able to kill the tuberculosis bacteria and by surgical removal of the upper third of one lung that had the greatest concentration of bacteria.

. Debi's warning about infectious diseases like TB is not to be fooled by little bacteria. In her words, they are "stubborn" and develop ways to survive. A scientist would say that bacteria rapidly evolve resistance to the drugs we use to treat infections caused by those organisms.

7. Point out to students that while it was appropriate to treat Debi with the antibiotics that are usually effective in treating TB, it is not appropriate to use antibiotics to treat illnesses that are caused by viruses. Elicit an explanation of the dangers of this practice by asking a question such as, "Although an antibiotic doesn't help you get over a viral infection, if you didn't know any better you might think it wouldn't do any harm. But you know better. Explain what negative consequences can result from inappropriate use of antibiotics."

Students should be able to explain that using antibiotics will select for bacteria that are resistant. Subsequent infections—either in the same person or in someone who is infected by the first person—will be caused by disease-causing bacteria that are resistant, and successful treatment will be much more difficult or even impossible. This line of logic requires extrapolation of the ideas students developed from their bacterial growth experiment and the Debi French story, so you may need to help them develop their explanation by giving them additional information and asking probing questions such as, "What if the antibiotic taken by a person who has a bacterial infection doesn't kill all of the disease-causing bacteria? What can you say about the bacteria that survive?" and "Research experiments have shown that harmless bacteria that become resistant to antibiotics can transfer that resistance to other bacteria, including disease-causing bacteria. How does this help explain why doctors don't want to prescribe antibiotics for viral infections?"

You may want to tell students that the evolution of antibiotic-resistant pathogens is a problem for treating more diseases than TB. For example, many strains of the organism that causes the sexually transmitted disease gonorrhea (Neisseria gonorrohoeae) and most strains of a common organism that causes many skin infections (Staphylococcus aureus) are now resistant to penicillin. Students consider a proposal to develop a new treatment for multiple-drug-resistant Staphylococcus aureus in Activity 5, Making Hard Decisions.

assessmentThis step provides an opportunity to evaluate students' understanding of the evolution of antibiotic resistance and its relevance to personal and public health.

8. Distribute one copy of Master 3.4, Antibiotic Concerns, to each team and assign one of the three statements to each team. Explain that each statement describes an example of an inappropriate or potentially inappropriate use of antibiotics. Instruct the teams to develop a brief public service announcement that would persuade the general public not to use antibiotics inappropriately. The announcement should be something that could be read on the radio, featured in a television commercial, or displayed on a public bulletin board. Collect the announcements and read several to the class; display all of them on a bulletin board in the classroom.

Laboratory Preparation for Activity 3

1. Four weeks before conducting the activity. Order the following materials from Carolina Biological Supply:

Allow two weeks for delivery. Carolina Biological Supply will only ship live or perishable materials on Mondays, Tuesdays, and Wednesdays.

2. Two days before conducting the activity. Prepare the following additional materials:

3. Prepare a stock solution of 25 mg/ml kanamycin in water and filter-sterilize it into a sterile test tube.

4. Prepare nutrient broth medium and nutrient agar plates following the directions on the packages. For medium containing kanamycin, aseptically add 2 ml of the stock kanamycin solution per liter of medium after the medium has cooled (but before the agar solidifies, in the case of plates).

5. Dispense 5-ml aliquots of nutrient broth into sterile, capped test tubes. You will need 2 test tubes of nutrient broth and 1 test tube of nutrient broth containing kanamycin for each team. You will also need 3 nutrient agar plates and 3 nutrient agar plates containing kanamycin for each team. We recommend preparing extras to allow for contamination and errors.

6. Inoculate 1 nutrient broth tube with P. fluorescens for each team 2 days before Day 1 of the activity (use a 0.1-ml inoculum). Incubate these cultures at 25°C.

If students are unfamiliar with aseptic technique, you will need to provide that instruction before they begin the experiment. You may want to demonstrate these techniques by showing the Day 1 segment of Bacterial Growth Experiment on the Web site. This segment shows students completing the first four steps of the experiment and observing aseptic techniques such as using sterile pipets, flaming the open mouth of a test tube before replacing the cap, and sterilizing and using a glass rod to spread a culture sample on a plate. The video also shows students observing safety practices such as tying back long hair, wearing lab coats and safety goggles, and washing their hands. Hands, equipment, and counter tops should be washed with a commercial, microbiological disinfectant, or with household bleach diluted 30-fold with water. You should also identify a place for students to discard their used cultures and explain that you will decontaminate all materials before disposal.

The P. fluorescens that is cultured in nutrient broth or on nutrient agar will grow up in 24 hours; however, the cultures in media containing kanamycin will take two or three days. We recommend that, after 24 hours of incubation, you refrigerate students' cultures in media without kanamycin (broth culture A and plates 1, 3, and 5). This will prevent overgrown cultures that may obscure the results.

All cultures should be decontaminated when students have completed their work. Used cultures should be placed in an autoclave at 1 atmosphere pressure for 15 minutes to kill bacteria. Plastic petri dishes should be placed in heat-resistant plastic bags prior to autoclaving because the dishes will melt and leak. A kitchen pressure cooker can also be used to kill bacterial cultures.

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