Antibiotic Lab: Title: Investigating the Effects of Various Antibiotics on Bacterial Resistance

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Clifton Hicks
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1 + Antibiotic Lab: Title: Investigating the Effects of Various Antibiotics on Bacterial Resistance

2 + Background Bacteria are single-celled prokaryotic organisms that lack a true nucleus and membrane-bound organelles. They have been a major cause of human infection and even death over the history of the interaction between the two. However most are not harmful to human health. Antibiotics are various chemicals used in medical science to kill bacteria. Penicillin is famous, among all antibiotics, for having been the first such wonder drug. Let s take a look at this important relationship.

3 + Background History

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5 + Background Antibiotic resistance is the effect of bacteria (and the colonies that they form) to resist or make ineffective the actions of a given antibiotic to kill them. Back to the future with antibiotic resistance 1

7 + Background Dates of Discovery for Commonly Used Antibiotics Ampicillin (1961, 1965) 1 Tetracycline (1953) 2 Penicillin (1929, 1940) 1

8 + Hypothesis (Prediction) Various questions could be posed regarding the relationship between three antibiotics (ampicillin, tetracycline, penicillin)and their impact on a single bacterium (Escherischia coli). For instance, does the age of an antibiotic make it more prone to being resisted by bacteria? As a team, create both a question and a hypothesis that you will investigate in this experiment. Be sure to follow proper formatting: If (MV) then ( RV) because (prediction reason)

9 + Overview of Experimental Design: Petri dish with E. coli Control Quadrant: No A, T, P T P A Experimental Quadrants: Ampicillin (A), Tetracycline (T) Penicillin (P)

10 + Experimental Design : Data Antibiotic disk Lawn of bacteria Zone of Inhibition (Z.I.) = Death Zone

11 + Experimental Design MV (IV): 3 types of antibiotics Ampicillin Penicillin Tetracycline RV (DV): Zone of Inhibition (Death Zone) in mm CVs: Petri dishes, agar, inoculating loops, temperature, etc.

12 + Materials Petri dish with agar gel (3) antbiotic paper disks Incubator (37 C) Inoculating loops Masking tape Gloves and goggles Forceps

13 + Assignment of Roles: Suggested Petri dish manager: responsible for labeling Petri dish and sealing it after inoculation Inoculator: responsible for inoculating the Petri dish with bacteria Antibiotic applicator: responsible for adding the antibiotic disks to the dish Coach/Data Collector: measures Z.I.

14 + Procedures (1 of 3) 1. Obtain a Petri dish full of agar and label properly. 2. Label the Petri dish along the edge or on the lid lacking agar (top) with the following: Your class period number and group number (Example: P1G3) Bacteria type Label each quadrant accordingly (A, T, P, C)

15 + Procedures (1 of 3) T C P A Be sure to label close to middle of dish in order to clearly see the Z.I.

quarter: Tetracycline (T) Penicillin (P)

Be sure to not do anything with the control

If all goes as planned there should be an

16 + Procedures (2 of 3) 3. Place one antibiotic disk in each remaining quarter: Tetracycline (T) Penicillin (P) Ampicillin (A) 4. Be sure to not do anything with the control group. If all goes as planned there should be an even lawn of bacteria growing on the dish. Tape both lids together with masking tape. NOTE: No ring around this antibiotic disk.

17 + Procedures (3 of 3) After 24 hours in the incubator set at 37º C 5. DO NOT OPEN YOUR PETRI DISHES!!! 6. Using a ruler measure the Zone of Inhibition and record in your group s data table. In addition, observe and record the color, relative size and shape of colonies you find. 7. Report your data on the class data table. 8. Dispose of your Petri dish as directed. 9. Complete the remaining sections of your lab report.

18 + Data Analysis Prepare a bar graph the class average of the Zones of Inhibition for each antibiotic tested.

19 + Interpretation & Conclusion Complete all three sections of the conclusion according to the document entitled Designing Experiments: Lab Write-Up Format

20 + Closure Possible class discussion questions: 1. The effectiveness of the different antibiotics on E.coli. Cite evidence. 2. Propose why one antibiotic or another is more effective. Consider their relative ages and antibiotic resistance. 3. Does the data suggest any trends in the effectiveness of the antibiotics? 4. Do you think populations of bacteria adapt over time to antibiotics? Does this relate to natural selection? 5. What exactly is going on in the zone of inhibition? 6. If you saw one colony growing in the zone of inhibition and streaked a plate with that colony, would the antibiotic be effective? Why?

21 + Works Cited 1. BMC Biology. (2014). Q&A: Antibiotic resistance: where does it come from and what can we do about it? Accessed on July 29, 2014 from: 2. Centers for Disease Control. Antibiotic Resistance Threats in the United States, Accessed on July 29, 2014 from: 3. Explorable. ( ). History of Antibiotics History Channel. (2014). Mankind the story of all of us: Penicillin. Accessed on July 29, 2014 from:

Controlling Bacterial Growth

Pre- Lab Discussion: Controlling Bacterial Growth Most bacteria (and other microorganisms) are harmless. In fact, many bacteria are beneficial. Cheesemaking, decay, and soil building are a few of the important