Combinatorial Chemistry is a technique used to synthesize a library of compounds and screen for a desired property. Instead of screening one compound at a time, the compounds are screened more efficiently in mixtures which maximize the use of resources while increasing the possibility of identifying an active compound. This is a key goal of the pharmaceutical industry and thus a common practice in Drug Discovery.
This lesson serves as a pre-lab activity in which students will gain valuable background knowledge as well as learn key skills that they will use to identify a potential drug that kills bacteria in a future lab series. Students will preview the methods used to test mixtures for antibiotic activity and to isolate individual compound components to confirm antibiotic properties. Finally, students will explore two critical techniques (Kirby-Bauer and Ouchterlony Assays) used both in the detection of antibiotic resistance and the identification of new compounds, using Combinatorial Chemistry, to combat address this growing public health threat.
Allow students to demonstrate mastery of the newly acquired skills or knowledge:
1. Students measure the zone of inhibition (ZOI) using the appropriate tools, methods and units.
2. Use standard ZOI chart to determine antibiotic susceptibility.
3. Use Kirby-Bauer assay ZOI results to determine best course of therapy for mock patients.
4. Extension: Identify class of microbe based on Kirby-Bauer assay results by performing a Gram-Stain.
NATIONAL BIOTECHNOLOGY STANDARD(S):
BT. 1.7 Demonstrate knowledge of standard precautions including proper storage, handling and disposal of biohazardous materials.
BT. 5.4 Apply the basic concepts of cell growth to manipulate cultures under aseptic conditions in the laboratory.
BT. 7.2 Research ethical issues presented by evolving science, including genetically modified foods, cloning, bioterrorism, gene therapy, and stem cells.
BT. 10.5 Demonstrate knowledge of the elements of scientific methodology, analysis of data, and developing conclusions (from laboratory assays such as the Gram-Stain and ZOI assay)
Engage (Activate Student Thinking)
1. What are the facts in this case?
2. How did we get here as a global health community?
3. Why are our antibiotics not working?
Explore (Guided/Student-Centered Activity)
Scenario: Imagine....you are a doctor in a country where TB infections have reached crisis levels. Although it was once treatable, now no patients respond to the first-line medications available.
Explain (Formulate Ideas)
Introduction to the Kirby-Bauer Assay
Now that a student's "need to know", in terms of how to address this global threat has been activated, explain the Kirby-Bauer Assay. Begin by explaining why the measurement of the Zone of Inhibition, when searching for new potential drug therapies such as Compounds A thru G on SLIDE 11, is so important and how this measurement is actually obtained (refer to SLIDE 10 and 15). After recording the measurements in the table on Page 3 and 4 of the student lesson guide, explain the relationship between the microbe which may possess the ability to survive in the presence of the antimicrobial agent and the mechanism of action and properties of many antimicrobial agents. Then determine if each result or the unknown microbes reaction to being exposed to the various antibiotics based on the measurements would be classified as resistant, intermediate, or susceptible.
Elaborate (Apply and Extend Understanding)
Whole Group Discussion:
1. Did any of the potential novel compounds possess antimicrobial properties? How did you arrive at this conclusion?
2. Based on the facts presented in this case, in the event a new drug is discovered, who should receive the promising new drug therapy first? Justify your recommendation!
As a group we view the video clip, "How a Drug Becomes a Drug" and pose a third and final inquiry.
3. Who, if anyone, owns the "rights" to novel compounds which are ultimately incorporated into new drug therapies? Apply information gained from the video clip as evidence to support your claim.
Evaluate (Monitor Understanding)
Scenario/Exit Ticket: You just hired a new biotechnologist in your hospital pathology lab...and there is much work to be done!! Quickly explain to your newbie how to conduct an antibiotic susceptibility test and the purpose for conducting this assay! (In other words, explain WHAT it is and WHY it is performed?)
Real World Connection
Instructors may extend the learning of antibiotic resistance and Combinatorial Chemistry by completing the Combi Chem Lab Series also posted here on BetterLessons. An overview of the Combi Chem Labs is outlined in a comprehensive PowerPoint Presentation in addition to the equations and required mathematical calculations which are previewed in student compound prep tables and data collection sheets.