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? ( F r om L a b o r at o r y M a n u a l & W or k b o ok i n M i c r o b i o l o gy A p p l i c at i o n s to P a t i e nt C are ( 9th e d .). B y J o s e p h i n e A . M o r e l l o , H e l e n E c k el M i z er, a n d P a u l A . G r a n ato C o p y r i g ht © 2 0 06 T he Mc G r a w - H i l l Co m p a n i e s , Inc. R e pri n t ed w i th p e r m i s s i on of T he Mc G r a w - H i l l Co m p a n i e s , I n c . ) 3. Why is iodine used to detect starch hydrolysis? 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? What kinds of precautions should be taken in caring for persons with d.

1. 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?

2. 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?
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3. Why is iodine used to detect starch hydrolysis?
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?
What kinds of precautions should be taken in caring for persons
with directly transmissible parasitic

10. infections?
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?
Week 5 Review Sheet I
Exercise 1: Hanging-drop and wet-mount preparations
1. How does true motility differ from Brownian movement?
2. What morphological structure is responsible for bacterial
motility?
3. Why is a wet preparation discarded in disinfectant solution
or biohazard container?
4. What is the value of a hanging-drop preparation?
5. What is the value of a wet-mount preparation?
Exercise 2: Simple stains
1. Define acidic and basic dyes. What is the purpose of each?
2. What is the purpose of fixing a slide that is to be stained?

11. 3. Why are the specimens to be stained suspended in sterile
saline or distilled water?
4. How does a stained preparation compare with a hanging
drop for studying the morphology and motility of bacteria?
5. List at least three types of bacteria whose names reflect
their shapes and arrangements, and state the meaning of each
name.
Exercise 3: Gram stain
1. What is the function of the iodine solution in the Gram
stain? If it were omitted, how would staining results be
affected?
2. What is the purpose of the alcohol solution in the Gram
stain?
3. What counterstain is used? Why is it necessary? Could
colors other than red be used?
4. What is the advantage of the Gram stain over a simple stain
such as methylene blue?
5. In what kind of clinical situation would a direct smear
report from the laboratory be of urgent importance?
Exercise 4: Pure bacterial colonies
1. When an agar plate is inoculated, why is the loop sterilized
after the initial inoculum is put on?
2. Distinguish between a pure culture and a mixed culture.

12. 3. Define a bacterial colony. List four characteristics by which
bacterial colonies may be distinguished.
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5. Why does the streaking method you used to inoculate your
plates result in isolated colonies?
Exercise 5: Pour plate and streaking technique to obtain pure
cultures
1. Discuss the relative convenience of pour- and streak-plate
techniques in culturing clinical specimens.
2. How do you decide which colonies should be picked from a
plate culture of a mixed flora?
3. Why is it necessary to make pure subcultures of organisms
grown from clinical specimens?

19. 4. What kinds of clinical specimens may yield a mixed flora in
bacterial cultures?
5. When more than one colony type appears in pure culture,
what are the most likely sources of extraneous contamination?