Solved by a verified expert:Hanging-Drop and Wet-Mount Preparations; Simple and Gram
Stains; and Pure Bacterial Colonies and Cultures
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?
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 Bram 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.
3. Define a
bacterial colony. List four characteristics by which bacterial colonies may be
4. Why
should a Petri dish not be left open for any extended period of time?
5. Why does
the streaking method used to inoculate 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
3. Why is it
necessary to make pure subcultures of organisms grown from clinical specimens?
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?