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Exercise 1: Moist and dry heat 1. How are microorganisms destroyed by moist heat? By dry heat?
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Cassandra Howery

Week 5 Assignment 2

Microbiology Laboratory

Week 5 Review Sheet II

Exercise 1: Moist and dry heat

1.  How are microorganisms destroyed by moist heat? By dry heat?

2.  Are some microorganisms more resistant to heat than others? Why?

3.  Is moist heat more effective than dry heat? Why?

4.  Why does dry heat require higher temperatures for longer time periods to sterilize than does moist heat?

5.                  What is the relationship of time to temperature in heat sterilization? Explain.

Exercise 2: The autoclave

1. Define the principles of sterilization with an autoclave and with a dry heat oven.

2. What pressure, temperature, and time are used in routine autoclaving?

3. What factors determine the time period necessary for steam-pressure sterilization? Dry-heat oven sterilization?

4. Why is it necessary to use bacteriologic controls to monitor heat- sterilization techniques?

5. When running an endospore control of autoclaving technique, why is one endospore preparation incubated without heating?

Exercise 3: Primary media for isolation of microorganisms

1. Define a differential medium and discuss its purpose.

2. Define a selective medium and describe its uses.

3. Why is MacConkey agar selective as well as differential?

4. Why is blood agar useful as a primary isolation medium?

5. What is the major difference between Modified Thayer-Martin (MTM) and chocolate agar? When would you use MTM rather than chocolate agar?

Exercise 4: Some metabolic activities of bacteria

1. What is the color of phenol red at an acid pH?

2. What is the function of a Durham tube?

4. How is indole produced in SIM medium? How is it detected?

5. How is hydrogen sulfide demonstrated in this medium? 

1. What is the advantage of viewing mold structures in a transparent tape preparation?

2. What fungus can be identified reliably by using the germ tube test?

3. Name three stains or reagents that may be used to facilitate the microscopic detection of fungi in clinical samples.

4. What is the main advantage of using the slide culture technique for identifying molds?

5. What is an opportunistic pathogen? Name three fungal specimens.

Exercise 6: Protozoa and animal parasites

1. Describe the basic structures of protozoa. Can these same structures be seen in bacteria using a light microscope?

2. Are any parasitic diseases directly communicable from person to person? If so, how are they transmitted?

3. What parasitic forms can be seen in the feces of a patient with hookworm?

4. Cryptosporidiosis? Tapeworm? Trichinosis?

5. What parasitic forms can be seen in the blood of a patient with African sleeping sickness? Filariasis?

Amebiasis?

6. What is meant by the “life cycle” of a parasite? What importance does it have to those who take care of

patients with parasitic diseases?

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