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40 2 50 -m i n ut e s e ss io G - to 51 ns The Full Course MOD EL IN ACTIVIT Y OVERVIEW SUMMARY Students model the effects of antibiotics on the population of the disease-causing bacteria during an infection. Students toss number cubes to determine whether an “infected patient” remembers to take the prescribed daily dose of antibiotics, which in turn affects the size of the bacterial population in the patient. The results demonstrate that it is critical to remember to take each dose on time and to complete the entire prescribed course of antibiotics. KEY CONCEPTS AND PROCESS SKILLS 1. Creating models is one way to understand and communicate scientific information. 2. Graphing data can reveal patterns that are not apparent from data tables. 3. Most infectious diseases are caused by microbes. 4. The human body has natural defenses against infectious diseases. These include barriers such as skin, linings such as mucus, and white blood cells in the immune system. 5. Antibiotics are effective against many bacterial infections, but not against viral infections. 6. Antibiotics can be effective against bacterial infections only if the entire course is completed as directed. A certain proportion of almost every naturally occurring population of disease-causing bacteria are resistant to (not easily killed by) antibiotics. Taking partial or incomplete courses of antibiotics actually increases the proportion of resistant bacteria in the population, and is thus harmful. Teacher’s Guide C-261 Activity 51 • The Full Course KEY VOCABULARY antibiotic infection bacteria resistant full course sample size immune system virus MATERIALS AND ADVANCE PREPARATION For the teacher * 1 Transparency 51.1, “Bacteria Graph Sample 1” 1 Transparency 51.2, “Bacteria Graph Sample 2” 1 overhead projector For each pair of students 1 set of 50 disks (20 black, 15 blue, 15 orange) * 4 colored pencils (including black, blue, orange) * 1 number cube For each student 1 Student Sheet 51.1, “Population Data” 1 Student Sheet 51.2, “Bacteria Graph” *Not supplied in kit TEACHING SUMMARY Getting Started 1. Briefly review the role of the immune system as the first line of defense against infectious diseases. Doing the Activity 2. The class reads the Scenario and the teacher models the Procedure. 3. Student pairs work together to collect data. Follow-Up 4. C-262 The class discusses the data and the relevance of sample size. Science and Life Issues The Full Course • Activity 51 INTEGRATIONS Mathematics Graphing bacterial populations over time reinforces the usefulness of graphing in visualizing trends in data. BACKGROUND INFORMATION Bacterial Resistance Bacteria, both beneficial and harmful, live within the human body. Infections occur when the size of a population of harmful bacteria (either indigenous or introduced) grows too large. Antibiotics have been extremely successful in fighting bacterial infections since their discovery in the 1930s. Today, many antibiotics are less effective because resistant bacterial strains have become more prevalent. Various antibiotics are used to effectively kill many different microbes. However, some microbes are resistant to these medicines. It takes only one resistant microbe within a population to lead to an increase in resistant microbes. As the rest of the bacterial population is killed off, the resistant bacteria face no competition and can reproduce more successfully. As a result, increased use of antibiotics can lead to the development (evolution) of resistant strains. The possibility that disease-causing organisms could become resistant to treatment with antibiotics was first observed in 1943, when penicillin was being developed for use. It was during the second clinical trial of penicillin that one of the 15 patients died from a strep infection because the microbe had become resistant to the antibiotic. Today, there are antibiotic-resistant strains of many different disease-causing microbes, including Streptococcus pneumoniae (which causes ear infections and meningitis), Mycobacterium tuberculosis (which causes tuberculosis), Haemophilus influenzae (which causes respiratory infections), and Neisseria gonorrhoeae (which causes gonorrhea), to name a few. More than 90 strains of Staphylococcus aureus bacteria, a common cause of hospital staph infections, are now resistant to penicillin. This is one reason it is important to reduce the unnecessary use of antibiotics and other antibacterial agents. Over-prescription and misuse contribute to the problem, and many health care providers are more carefully monitoring their use of antibiotics. Some researchers are also recommending that the routine use of antibacterial soaps and other such products be reduced. One interesting side note is that over 40% of the Teacher’s Guide C-263 Activity 51 • The Full Course antibiotics manufactured in the U.S. are given to animals, often for reasons other than infections. The use of antibiotics in agriculture can also contribute to the rise of antibiotic-resistant microbes. Patients have played, and continue to play, an important role in the developing crisis. Many people who have been given prescriptions start feeling better after a few days and stop taking the antibiotic. All of the microbes may not yet have been killed, especially those with more antibiotic resistance. These still-living resistant bacteria then reproduce. This increases their population and increases the chance of their causing future infections that cannot be treated with a typical course of antibiotics. However, this crisis is not due to patients alone. Health care policies have also contributed. In some countries, many antibiotics are available without a prescription and thus the opportunity for misuse in these areas is even greater. In some cases, doctors have prescribed antibiotics unnecessarily, either as a placebo or because patients demand them. As more and more antibiotics are prescribed, the non-resistant strains are killed, allowing the population size of the resistant strains to increase, especially as they are passed from individual to individual. REFERENCES Levy, Stuart B. “The Challenge of Antibiotic Resistance.” Scientific American (March 1998). Radetsky, Peter. “Last Days of the Wonder Drugs.” Discover (November 1998): 76–84. C-264 Science and Life Issues The Full Course • Activity 51 DOING THE ACTIVIT Y TEACHING SUGGESTIONS 2. GETTING STARTED 1. The class reads the Scenario and the teacher models the Procedure. Briefly review the role of the immune Ask students to read the Scenario titled “A Bacterial system as the first line of defense against Infection” on page C-100 in the Student Book. infectious diseases. While they are doing this, distribute the materials, Briefly review that an organism’s immune system is constantly attacking and removing potentially harmful substances. Point out that medicines are needed only in situations where the immune sys- including Student Sheet 51.1, “Population Data.” You can also provide Student Sheet 51.2, “Bacteria Graph,” at this time, or wait until students have completed collecting their data. tem is not able to get rid of the infection. This can Review what each disk color represents and then occur if the immune system is not functioning as review the Procedure. Depending upon the makeup well as it could be, or if the infection is too wide- of your class, you may want to lead the class step-by- spread for a properly functioning immune system step through the Procedure. Make sure that students to combat. understand that at the start, their body is infected Ask students to recall that disease-causing bacteria can cause infections and that antibiotics can be used to kill these bacteria. Ask students to share their experiences with antibiotics: What illness was being treated? What kind of antibiotic was used? What was the length of treatment? Did the antibiotic work? Was all of the medicine used? Ask students what they think their parents or the general public know about proper antibiotic use. Some students may be familiar with the recommendation that the full course of antibiotic be taken, while others may not. with only 20 bacteria, not all 50 they were given. You might want to suggest that they draw a circle representing the body on the bottom of Student Sheet 51.1 and place the initial 20 disks inside the circle. It is also recommended that you explain the Number Cube Key on page C-101 in the Student Book so that all student pairs understand what to do after each toss of their cube. 3. Student pairs work together to collect data. Encourage student pairs to begin working on their own. Circulate among the groups to make sure each pair is doing the simulation correctly. Once students Explain to the class that in this activity they will be have proceeded to the last step, you may have to pro- modeling the effects of antibiotics on a population of vide assistance with the graphing. Again, depending disease-causing bacteria living inside a sick person. upon the makeup of your class, you may want to work through this step with the entire class. Alternatively, if students are skilled at graphing, use the Teacher’s Guide C-265 Activity 51 • The Full Course AND Point out that, in this model, the small sample size C O N D U C T I N G I N V E S T I G AT I O N S (DCI) variable to of the class data is relevant. Ask students, What score students’ work on Student Sheet 51.2. other factors may act as variables in the effective- Organizing Data element of the D E S I G N I N G ness of an antibiotic? In reality not every infection FOLLOW-UP 4. The class discusses the data and the relevance of sample size. will respond to an antibiotic in the same way. There is no way to know whether the population of disease-causing bacteria you are treating will be controlled more or less quickly by the antibiotic than Once all groups have finished their graphs, use a expected. Ask students, If you have an infection, is show of hands to determine how many student there any way for you to know if you have killed all pairs killed all the harmful bacteria in their body. of the disease-causing bacteria most of the way Results will indicate that in order to be certain that through your full course of antibiotic? If some stu- the antibiotics destroy the bacteria, especially those dents are confident that they could determine this, organisms most resistant to the effects of the antibi- ask, What are the consequences if you are wrong? otics, it is critical to remember to take each dose on Point out that antibiotic treatments often require time and to complete the entire prescribed course of taking medicines for several days longer than may antibiotics. (However, an occasional student group be required, to prevent an increase in the proportion will “forget” only one dose late in the treatment and of more resistant bacteria in the population—a risk still eradicate all of the bacteria. See the discussion of which can exist even if no doses are omitted. below regarding the idealized nature of the model.) Briefly discuss these results or use Analysis Questions 1 and 2 as a prompt for a full class discussion. n Teacher’s Note: When discussing Analysis Ques- Raise issues from the “Studying People Scientifically” unit of Science and Life Issues on the variability of individual response and the difficulty of predicting precisely how a drug might affect an individual. tion 2(c), remind students that this activity is a Also suggest the possibility of immediate reinfec- model, and note that the example of three bacteria tion (there may be bacterial sources in the environ- is based on this simplified model. ment as a person begins to recover). A more resis- Two possible data sets and their associated graphs are provided on Transparencies 51.1, “Bacteria Graph Sample 1,” and 51.2, “Bacteria Graph Sample 2.” The first set of data shows that the bacteria are completely eradicated after seven doses if none of the doses are forgotten; the second set shows the tant starting bacterial population, such as may be likely to result from a reinfection, could be modeled by increasing the proportion of orange disks in the initial population. Bring closure to the discussion by emphasizing the importance of taking the full course of any antibiotic prescribed. dramatic increase in the proportion of extremely Analysis Question 4 can be assessed with the resistant bacteria in the population that results U N D E R S TA N D I N G C O N C E P T S (UC) scoring guide. when two doses are forgotten. C-266 Science and Life Issues The Full Course • Activity 51 SUGGESTED ANSWERS ing, and thus the only ones able to infect oth- TO ANALYSIS QUESTIONS ers, are the extremely resistant bacteria (orange 1. disks). Did the antibiotic help you to completely kill all of the harmful bacteria living in your body? c. Explain. Suppose most infected people stopped taking the antibiotic when they began to feel better. (For example, consider the point in the simulation Answers will depend on the number of times stu- when there were only three harmful bacteria dents “forgot” to take the antibiotic (as a result of left.) What do you predict might happen to an tossing a “2”or a “4”). Students who never forgot antibiotic’s ability to kill the harmful bacteria the antibiotic will be able to kill all the harmful bacteria with the 7th dose. Point out that most if the infection returns? Explain your reasoning. antibiotics are prescribed with a dose or two It could decrease. Over time, the population of beyond what might be sufficient, in case the bac- harmful bacteria would contain proportionally teria are a more resistant than is typical. more of the extremely resistant bacteria than the n Teacher’s Note: If students forget just one dose, in other types. Since the extremely resistant forms some cases they will be able to get rid of the diseasecausing bacteria by the end of the 8th dose . If they population as a whole becomes increasingly are more difficult to treat with the antibiotic, the antibiotic-resistant. forget more than one dose (e.g., see Transparency 51.2, “Bacteria Graph Sample 2”), in all cases they will have some disease-causing bacteria living in 3. Use your graph to describe how the population of each type of bacteria changed over their body at the end of the full course of antibiotics. the course of the antibiotic treatment. 2. a. Imagine infecting someone else immedi- When the antibiotic is first taken, the total pop- ately after catching the infection (before ulation and the population of the least resistant you started taking the antibiotic). With what type bacteria decrease while the populations of the of bacteria would you be most likely to infect more resistant bacteria increase. In fact, even in them? the situation where no doses are missed, the Initially, the most abundant bacteria are the population of the extremely resistant bacteria continues to increase until the 6th dose. This least resistant bacteria (black disks); therefore, they are the ones most likely to infect someone else. b. may surprise to many students, and is in fact a shortcoming of the model. With continued regular doses, the populations of the more resistant Imagine infecting someone else near the end of bacteria also begin to decrease until eventually your antibiotic course. With what type of bac- all the bacteria are gone. Any missed doses teria would you be most likely to infect them? result in increases in the populations of those Unless you skipped many doses, near the end of your antibiotic course the only bacteria remain- bacteria strains that are living in the body at that time. Teacher’s Guide C-267 Activity 51 • The Full Course n Teacher’s Note: Students will notice that in this microorganisms. Also, although many people scenario, it is highly likely that at least one dose is do forget to take their medicine regularly, most skipped in the course of eight tosses. (In this case, of them do not do it on purpose, and tossing tossing a cube to simulate remembering vs. forget- the cube models the random nature of forget- ting to take the antibiotic assumes a probability of fulness. In addition, the fact that not taking 1/3 that a patient will forget a “dose.”) The distrib- antibiotics as prescribed can result in increasing ution of results would change markedly if the prob- the proportion of an antibiotic-resistant strain ability of forgetting were changed significantly. in a population is demonstrated. 4. Why is it important to complete the However, the activity does not model what UC might happen if you completely stopped taking full course of an antibiotic as prescribed? the antibiotic as you began to feel better, or if you A complete and correct level 3 response follows: You have to take the amount of antibiotics also indicates that a population of 20 disease- your doctor prescribes. If you take only some causing bacteria would warrant the use of an of them, the extremely resistant bacteria will antibiotic. An actual bacterial infection would keep increasing. Your body needs the antibi- involve thousands of bacteria. (In addition, the otics to help fight off the disease-causing bac- model suggests that an antibiotic systematically teria. If you take the antibiotics for two days kills more and more resistant strains of bacteria and then forget for a couple of days, you fight in succession; in fact, the more resistant a bac- some of the bacteria, but some will keep grow- terium, the more likely it is to survive for a peri- ing, especially the more dangerous ones. This od of time in the presence of antibiotic.) means you could still be sick or even get sicker in the long run. 5. took multiple doses at the same time. The model 6. You find out that you have a viral infection and not a bacterial infection. What would happen to the Was this activity a good model of an antibiotic amount of virus in your body each time you took the treatment? Explain. antibiotic? Explain. The strengths of this model include the fact Nothing would happen as a result of taking the that it takes a course of antibiotics taken over antibiotic. This question reinforces the idea that time to kill a population of disease-causing antibiotics do not work against viral diseases. C-268 Science and Life Issues Name Date Population Data Table 1: Number of Harmful Bacteria in Your Body Toss Number Least Resistant Bacteria (black) Resistant Bacteria (blue) Extremely Resistant Bacteria (orange) Initial 13 6 1 Total 20 1 2 3 4 5 6 7 ©2006 The Regents of the University of California 8 Science and Life Issues Student Sheet 51.1 C-269 Name Date Bacteria Graph 30 Number of bacteria 25 20 15 10 5 ©2006 The Regents of the University of California 1 2 3 4 5 6 7 8 Time (in days) Key Least resistant bacteria = Resistant bacteria = Extremely resistant bacteria = Total number of bacteria = Science and Life Issues Student Sheet 51.2 C-271 Bacteria Graph Sample 1 Number of bacteria 20 Key Least resistant bacteria = Resistant bacteria = Extremely resistant bacteria = Total number of bacteria = 15 10 5 0 1 2 3 4 5 6 7 8 Time (in days) Transparency 51.1 Bacteria Graph Sample 1 ©2006 The Regents of the University of California Toss Number Least Resistant Bacteria Resistant Bacteria Extremely Resistant Bacteria Total Initial 13 6 1 20 1 8 6 1 15 2 4 7 2 13 3 0 8 3 11 4 0 4 4 8 5 0 0 5 5 6 0 0 1 1 7 0 0 0 0 8 Key Science and Life Issues Transparency 51.1 Least resistant bacteria = Resistant bacteria = Extremely resistant bacteria = C-273 Bacteria Graph Sample 2 Number of bacteria 20 Key Least resistant bacteria = Resistant bacteria = Extremely resistant bacteria = T Total number of bacteria = 15 10 5 0 1 2 3 4 5 6 7 8 Time (in days) Transparency 51.2 Bacteria Graph Sample 2 ©2006 The Regents of the University of California Toss Number Least Resistant Bacteria Resistant Bacteria Extremely Resistant Bacteria Total Initial 13 6 1 20 1 8 6 1 15 2 4 7 2 13 3 (forgot) 5 8 3 16 4 1 9 4 14 5 0 7 5 12 6 (forgot) 0 8 6 14 7 0 4 7 11 8 0 0 7 7 Science and Life Issues Transparency 51.2 C-275