Evolution of Antibiotic Resistance



Evolution of Antibiotic ResistanceIntroductionBacteria are everywhere. While many are beneficial, there are a few that can cause serious harm to other organisms such as humans. Usually our immune system is able to fight off bacterial infections, but not always. As a response, humans have discovered chemical compounds known as antibiotics which can kill these harmful bacteria. Over time, many antibiotics have lost their effectiveness. These activities explore how bacteria evolve resistance.Essential Questions:1. How do bacteria evolve to have antibiotic resistance?2. How does knowledge of evolution help in our battle against harmful bacteria?3. What can we do to curb antibiotic resistance?SafetyFollow standard laboratory procedures as required.MaterialsBingo chips (blue, yellow and red)DiceColored pencilsSmall paper bagsProcedurePart I Modeling ResistanceImagine you are sick with a bacterial infection and a doctor has prescribed an antibiotic. You are to take this antibiotic once every day for eight days. The colored disks represent the bacteria in your body. The blue disks are least resistant, the yellow are resistant and the red are highly resistant to the antibiotic. Sometimes you might forget to take your pill. What will happen?You will work with a partner to collect data. Begin with 20 total disks: 13 blue, 6 yellow and 1 red. These disks represent the bacteria causing the infection in your body. Record this as the Initial population on Table 1.2. Time to take your pill! Roll the dice and follow the directions on the Dice Key on the data sheet:3. Record the number of each type of bacteria now in your “body” in Table 1.4. The bacteria are reproducing! If one or more bacteria of any color are still alive add one disk of that color to your population. (For example, if you have 8 blue, 4 yellow and 1 red bacteria; add one blue, one yellow and one red disk to your population)5. Repeat steps 2-4 until you have completed Table 1.6. Use your data in Table 1 to graph the population of each type of bacteria and the total number of bacteria through time.7. Share your results with some of the groups nearby. Answer the analysis questions for Part I.Part II Modeling gene transferBacteria “reproduce” by binary fission. This type of reproduction means that the genes in the daughter cell(s) are the same as those in the parent cell. As a result bacteria have evolved interesting ways of sharing genetic information. One of which is conjugation were two cells join together via a tube called a pilus and genetic material in the form of plasmids is exchanged. The class will be divided up into bacteria (brown bag) and a few antibiotics (medicine capsule). Antibiotics will be given secret instructions by the teacher. 1. Bacteria will first conjugate. Each bacterium will pair with another bacterium. Do not look in each other’s bag. Reach out your arm (pilus) and grab five beads (plasmids). The other bacteria will do the same. Once you have both gotten your beads put them into your bag.2. Release the antibiotics! Each antibiotic will pick a bacterium to “attack” by looking in the bacterium’s cell (brown bag). The antibiotics will follow the secret instructions given to them by the teacher and either release the bacteria or escort it to the morgue. Your teacher will tally the number of live and dead bacteria.3) Follow steps 1-2 three more times.4) After the fourth round look at the beads in your bag. Count how many of each color you have and report it to your teacher. Return your bag and beads or medicine capsule. Return to your seat and record the data on the board into data Table 2 and Table 3.Part III Graphing DataIn the table on your data sheet is real data collected from a community in Finland from 1978-1993. The first column is the year. The second column is the defined daily dose (DDDs) per 1,000 inhabitants, per day, of antibiotics given to children with middle ear infections. The last column is the percent of resistant strains of bacteria found when children’s ears were cultured. Make a graph with two lines--one showing Antibiotic Use (DDD) vs. Year and one indicating Percent Resistant Strains vs. Year. You will need two y-axes, one for each dependent variable.Part IV Antibiotic timelineYour teacher will assign you an antibiotic. Use books or web resources to research the assigned antibiotic. Include the name of the antibiotic, when it was discovered, who discovered it, how it works (mechanism of action), and when resistance to it was first found. Enter this information in Table 4. When instructed, add the name of the antibiotic, the discovery date and the date resistance was found to the timeline. Fill in the remainder of Table 4 using the information gathered by the other groups.Student Data Sheet Name:_____________________________Antibiotic ResistancePart IDate: _____________________________Dice KeyYour RollWhat HappenedWhat to Do1, 3, 5, 6You took your antibiotic on time, so bacteria are being killed!Remove 5 disks: Start with the blue disks, then yellow, then red2, 4You forgot to take your antibiotic.Do nothing.Table 1. Number of Harmful Bacteria in Your BodyRoll NumberLeast Resistant Bacteria (blue)Resistant Bacteria(yellow)Highly ResistantBacteria (red)TotalInitial12345678Graph 1.Questions Part I1. Did the antibiotic kill all of the harmful bacteria in your body?2. Did you “forget” to take any pills? Did any of the groups near you miss a dose? How do your results compare? Refer to your data in your answer.3. Imagine a friend came to visit you on the first day you took your antibiotics. If they catch your illness what strain of bacteria would most likely infect them? Why?4. Imagine another friend came to visit on day seven. If they catch your illness what strain of bacteria would most likely infect them? Why?5. Suppose most people start to feel better when there are only a few bacteria left (around 3 total) in their body and stop taking their antibiotics. How well do you predict the same antibiotic will work if the infection returns?6. Why is it important to take the full course of an antibiotic when prescribed? Use evidence to support your answer.Student Data Sheet Name:_____________________________Antibiotic ResistancePart IIDate: _____________________________Table 2. Surviving bacteriaRound #1234Number of bacteriaaliveTable 3. Class results of plasmid exchangeDead BacteriaLive Bacteria# light beads# dark beads# light beads# dark beadsQuestions Part II7. What did the beads in your bag represent? Did everyone have the same kind?8. What does your outstretched arm represent? Is this a good model for conjugation?9. What color “plasmid” is needed for a bacterium to survive? How many?10. What are some other ways bacteria might gain resistance?11. What was missing from this simulation?12. What do you think happens to the beneficial bacteria in your body when you take antibiotics? What might this do?Student Data Sheet Name:_____________________________Antibiotic ResistancePart IIIDate: _____________________________Table: Antibiotic Use in FinlandYearDDD% Resist. Strains19780.84019790.92219801.042919810.984619821.024519831.035819840.956119851.126019861.064919871.145919881.215819891.287119901.328419911.317919921.277819931.2891Graph 2.Questions Part III13. Refer to the Antibiotic Use in Finland table and your graph. Has the amount of antibiotic used in this example increased, decreased or stayed the same over time?14. Has the percent of antibiotic resistant bacteria in this example increased, decreased or stayed the same over time?15. Based on these data do you think these two factors (DDD and % resistant) are related? If so how?Student Data Sheet Name:_____________________________Antibiotic ResistancePart IVDate: _____________________________Table 4.Antibiotic nameDiscovery dateDiscovered byMechanism of actionResistance discovery datePenicillinStreptomycinTetracyclineErythromycinVancomycinMethicillinCarbapenemGentamicinLinezolidCiprofloxacinDaptomycinAmpicillinAmoxicillinQuestions Part IV16. How long have antibiotics been in use?17. How were the first antibiotics discovered? When was the first case of resistance reported?18. What antibiotics no longer work? 19. Why do we have to keep developing new antibiotics?20. Explain what will happen if all antibiotics stop working?21. List 2 ways that we can prevent antibiotic resistance.22. Some farmers give small doses of some of the same antibiotics used in humans to farm animals such as pigs, cows and chickens. Often they are just used to make the animals grow faster. Why might this be a bad idea?23. Should we give antibiotics to non-life threatening maladies such as ear infections? Argue why or why not.24. Recall the steps needed for evolution to occur by natural selection; there must be variation in a population, there must be a selective pressure, some variants must survive or reproduce better, the selected traits must be heritable. Do we have enough evidence to show that bacteria have evolved antibacterial resistance? Use evidence you gathered in this activity to argue your case. ................
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