Biology Commonwealth of Virginia
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- The Germ Theory of Infectious Disease and Koch’s Postulates
- Materials needed
- Instructional activity
- Introduction
- Observations and Conclusions
- Sample assessment
- Follow-up/extension
Name: Date:DirectionsState at least one function for each organ listed below, and indicate the system (transport, endocrine, excretory, nervous, digestive, etc.) to which the organ belongs:
The Germ Theory of Infectious Disease and Koch’s PostulatesOrganizing Topic Life Functions and Processes Overview In this microbiology laboratory activity, students test each of Koch’s Postulates. They use fruit and fruit mold to simulate diseased host organisms and the pathogens or infectious agents that cause the disease. During the incubation time, students make observations and record changes in the mold growth. Related Standards of Learning BIO.1a, c; BIO.2c; BIO.5e ObjectivesThe students will discuss the major factors that impact human health, including microorganisms environmental influences; recognize that the acceptance of the germ theory of disease has resulted in a modern emphasis on sanitation, including safe handling of food and water aseptic techniques development of vaccines chemicals and processes to destroy microorganisms. Materials neededCopies of the attached student data sheet For each lab group: Postulate 1: 3 oranges Culture of Penicillium italicam, grown on potato dextrose agar Beaker or jar large enough to hold two oranges Dissecting needle Bunsen burner 10% bleach solution in a container Cool, soapy water Clean scrub brushes Fine-point permanent markers Graph paper with 1 cm squares Zip-top bags Postulate 2: Sterile swab Petri dish of potato dextrose agar Postulate 3: 3 oranges Dissecting needle Bunsen burner 10% bleach solution in a container Cool, soapy water Clean scrub brushes Fine-point permanent markers Graph paper with 1 cm squares Zip-top bags Postulate 4: Sterile swab Petri dish of potato dextrose agar Instructional activityContent/Teacher NotesDiseases can be spread by air, water, food, and human and animal vectors. In 1854, John Snow, a Westminster physician, found a relationship between polluted water and disease. Then in 1884, Robert Koch, a German microbiologist, isolated from water taken from Germany’s Elbe River the bacteria Vibrio cholera, which cause cholera. This proved the relationship between polluted water and disease. Koch went on to formulate an established set of procedures to isolate and identify the causative agent of a particular microbial disease. The following four steps, which are still used today, are known as Koch’s Postulates: 1. A specific organism must always be observed in association with the disease. 2. The organism must be isolated from an infected host and grown in pure culture in the laboratory. 3. When organisms from the pure culture are inoculated into a susceptible host organism, it must cause the disease. 4. The infectious organism must be re-isolated from the diseased organism and grown in pure culture. In this microbiology laboratory activity, students will test the four postulates established by Koch. They will observe and record mold growth on fruit and in a laboratory Petri dish. From these observations, they will determine whether the mold grown on the fruit and in the Petri dish is the same mold, thus proving Koch’s postulates. They will learn beginning aseptic laboratory technique and isolation of a microorganism. Instructor directions for incubating the oranges and measuring the mold growth are as follows: 1. Using the graph paper, use a fine-point permanent marker to draw a 10 x 10 cm grid on each zip-top bag. This grid will serve for counting a representative sample of the mold on each orange. 2. Place the inoculated oranges inside the zip-top bags, but do not seal. The bags must remain aerobic during the incubation time. At the end of the incubation period, the bags will be sealed to minimize spore dispersal during counting. 3. Line up the 10 x 10 cm grid with a representative part of the orange. Count the number of squares where the mold is apparent as fuzzy colonies of white or blue-green. The number can be recorded on the data table as an actual count (x) ÷ 100 cm, or as a percent. Because mold growth is slow, the actual in-class time spent will be minimal after the initial laboratory setup. The laboratory activity will take place over a minimum of four weeks, depending upon the amount of time needed for the mold, Penicillium italicam, to grow and sporulate. This amount of time will depend upon the viability of the culture and the warmth of the incubation area. Students will monitor and record daily the changes in the oranges and PDA plates. They will record mold growth when approximately half of the observable mold has sporulated (changed from fuzzy white to blue-green). During this incubation time, students will be introduced to the Germ Theory of Infectious Disease. The Department of Epidemiology at UCLA has an interactive Web site (http://www.ph.ucla.edu/epi/snow.html) that shows students the effects of widespread epidemics and how deadly microbial diseases were during these epidemics. You may also choose to introduce the following topics to enhance this microbiology laboratory activity. Planning investigations, formulating hypotheses, testing hypotheses (BIO.1) Classification of microorganisms, including eubacteria, archaea, and fungi (BIO.5) Characteristics and growth of fungi (BIO.5) Eukaryotic and prokaryotic cells and viruses (BIO.4, 5) Limiting factors for growth of microorganisms (BIO.5) Contributions of scientists, such as John Snow, Robert Koch, and Louis Pasteur (BIO.2) Introduction1. Have students use the Web site mentioned above to read “John Snow” and “The Handle” and watch “The Broad Street Pump Outbreak.” 2. Introduce students to Koch’s Postulates, and discuss how these helped to explain epidemics of microbial diseases. 3. Explain to students that they will test each of Koch’s Postulates, using fruit and fruit mold to simulate diseased host organisms and the pathogens or infectious agents that cause the disease.
ProcedureHave students work in groups of two or three to accomplish the following steps: Postulate 1 1. Clean lab tops with disinfectant or bleach solution. 2. Obtain three oranges. Wash two oranges with cool, soapy water. Scrub oranges thoroughly with scrub brush. Rinse in clear running water. Set aside the unwashed orange. 3. Place the two washed oranges in a large beaker or jar. Cover with a 10% bleach solution, and let stand for 10 minutes. 4. Rinse the bleached oranges in clear running water for 10 minutes. 5. Place the dissecting needle into the flame on the Bunsen burner and allow it to cool. Pierce the skin of both bleached, rinsed oranges three or four times with the needle. 6. Flame the mouth of the tube containing the Penicillium italicam and, using a sterile swab, aseptically remove a small sample of the culture and smear it over the puncture wounds in one orange. Do not inoculate the other punctured orange. 7. Place both oranges in separate gridded zip-top bags. Label all three bags with three labels: Bleached” or “Unbleached,” “Punctured” or “Unpunctured,” “Inoculated with Mold” or “Uninoculated with Mold.” Also, put the date on all three bags and the initials of group members. The bags will be allowed to remain at room temperature for about a week. 8. Record daily observations on a data table. When the fuzzy white mold turns blue-green/green, the mold has sporulated and can be isolated and grown in pure culture on a special agar — potato dextrose agar (PDA).
1. Clean lab tops with disinfectant or bleach solution. 2. Obtain a Petri dish of potato dextrose agar. Label the bottom (agar side) of the plate with the date and group initials. 3. Using a sterile swab, transfer some of the mold spores (blue-green/green) onto the plate of potato dextrose agar. Hold the Petri plate lid at 45˚ angle to protect the agar from contamination during the spore transfer. Streak across the plate in a zigzag manner until the entire plate has been streaked. 4. Incubate the plates upside down at room temperature for one week or until the mold produces spores. 5. Record daily observations on a data table. When the culture on the PDA plate has sporulated, refrigerate plate, and proceed with Postulate 3. Postulate 3 1. Clean lab tops with disinfectant or bleach solution. 2. Obtain two oranges, wash, and rinse. Follow instructions for Postulate 1, steps 3 through 8, using the spores from the PDA plates. Refrigerate plates for comparison for Postulate 4.
1. Clean lab tops with disinfectant or bleach solution. 2. Follow instructions for Postulate 2, steps 2 through 5, using spores from this diseased organism to be grown in pure culture on the PDA plate.
2. Use the following activity questions to lead students into drawing conclusions: Aseptic laboratory procedures: Why are lab tops disinfected? Why are the dissecting needles flamed? Why should the oranges be scrubbed? What was the purpose of putting the oranges in the bleach? Koch’s Postulates: Why have Koch’s Postulates remained unchanged since 1884? What did the oranges and the mold represent, using the terminology from Koch’s Postulates? Did the same mold infect the organism the second time? Support your answer, using your data table. Germ Theory of Infectious Disease: What is the “miasma” theory of infectious disease? What is the “germ” theory of infectious disease? When the outbreak of cholera around the Broad Street pump occurred, what did Dr. John Snow do to the pump? How did the scientific community react when Dr. Snow published his findings? Discuss the significance of John Snow’s work. 3. Have students read the article at http://www.nesc.wvu.edu/ndwc/ndwc_DWH_2.html. What kinds of changes took place in municipal water supplies as a result of John Snow’s work? Sample assessmentHave students write a paragraph describing a childhood disease they may have had. They should include where they contracted the disease, whether they gave it to anyone else, how it is transmitted, and how they would protect others from getting it. Follow-up/extensionHave students answer the following questions about Experimental Design (BIO.1): In testing Postulate 1, what did the unwashed, unbleached, unpunctured, and uninoculated orange test? For Postulates 1 and 3, what did the washed, bleached, punctured, but uninoculated orange test? What were the constants in this experiment? What was the independent variable (IV) for each postulate? Dependent variable (DV)? Have students formulate a hypothesis for each postulate. Have students invent a method to measure accurately the amount of mold growth on 1) an orange and 2) a Petri dish. Triclosan and Disease: Research a common ingredient in antibacterial soap, describing its uses and discussing any problems that may be associated with its use. The following Web site may be helpful: http://antoine.frostburg.edu/chem/senese/101/consumer/faq/triclosan.shtml. Directory: testing -> sol -> scope sequence scope sequence -> History and Social Science Standards of Learning Enhanced Scope and Sequence sol -> Strand Earth Patterns, Cycles, and Change Topic Investigating fossils in sedimentary rock Primary sol testing -> Prairie State Achievement Exam testing -> Testing and Assessment updated Tentative schedules testing -> Local unit tests Located at module-name sol -> P. O. Box 2120 Richmond, Virginia 23218-2120 sol -> Strand Interrelationships in Earth/Space Systems Topic Investigating ocean currents Primary sol sol -> History and Social Science Standards of Learning for Virginia Public Schools Wo Board of Education Commonwealth of Virginia March 2015 History and Social Science Standards of Learning for Virginia Public Schools Adopted in March 2015 by the Board of Download 3.95 Mb. Share with your friends:
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