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Parasitology [LAB] > EXERCISE 5: > Flashcards

EXERCISE 5: Flashcards

1
Q

is a routine part of parasitologic procedures that allows the detection of small numbers of parasites that may be missed by using only a direct fecal smear

A

stool concentration technique

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2
Q

is indicated when the direct wet mount examination is negative despite the clinical symptoms indicating parasitic infection of a patient.

A

stool concentration technique

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3
Q

Technically, the purpose of stool concentration is to

A

aggregate parasites
remove as much debris as possible

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4
Q

Concentration techniques can be performed on

A

fresh or preserved stool specimens

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5
Q

may be recovered by concentration

A

Helminth eggs and larvae, and protozoan cysts

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6
Q

will not be seen as they are usually destroyed during the concentration procedure

A

protozoan trophozoites

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7
Q

two types of stool concentration procedures:

A

(1) sedimentation
(2) flotation

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8
Q

are designed to separate parasites from fecal debris by centrifugation and/or differences in specific gravity

A

(1) sedimentation
(2) flotation

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9
Q

is accomplished by suspending the fecal specimen in water or aqueous solution of low specific gravity and allowing natural settling to occur, or accelerating the process by centrifugation, leaving the parasites at the bottom of the suspension

A

Sedimentation technique

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10
Q

permits the separation of protozoan cysts and certain helminth eggs from excess debris through the use of a liquid with a high specific gravity

A

Flotation technique

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11
Q

The parasites, by their buoyancy, are recovered in the (?), and the debris remains in the bottom of the tube.

A

surface film

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12
Q

more efficient and easier to perform accurately

A

sedimentation technique

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13
Q

is the most widely used sedimentation technique

A

Formalin – ether sedimentation procedure

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14
Q

It is approved and recommended by the Department of Health for screening food handlers and Overseas Filipino Workers (OFW).

A

Formalin – ether sedimentation procedure

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15
Q

As a sedimentation technique, its principle is based on

A

specific gravity

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16
Q

is added to a formalin-fixed sample and the tube is then centrifuged

A

Ether

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17
Q

are heavier than the solution and settle in the sediment of the tube

A

Parasites

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18
Q

is usually lighter and rises to the upper layers of the test tube

A

fecal debris

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19
Q

The tube is then decanted and the sediment is examined in a

A

wet preparation, unstained (i.e., with saline) and/or with iodine

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20
Q

A (?) of fresh stool is mixed with Formalin (5-10%). Too much or too little specimen will result in an ineffective concentration.

A

half-teaspoon

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21
Q

The stool-formalin mixture is allowed to stand a minimum of (?) before straining through a gauze for adequate fixation/preservation of parasites, if there’s any.

A

30 minutes

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22
Q

When vigorously shaking the tube for (?) after the addition of ether, exert pressure on the stopper throughout and hold the tube so the stopper is directed away from your face.

A

10 seconds (up to 30 seconds)

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23
Q

is used as an extractor of debris and fat from the feces and leaves the parasites at the bottom of the suspension.

A

Ether (ethyl ether)

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24
Q

is widely recommended as a substitute for ether which is an explosive and flammable compound.

A

Ethyl acetate

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25
Q

Ethyl acetate is used the same way in the procedure and is much safer, and more efficient for recovery of (?) and as well as eggs from (?) and (?)

A

Giardia lamblia cysts
Taenia sp.
Hymenolepis nana eggs

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26
Q

Wait for (?) before the stopper is carefully removed to prevent explosive release of pent-up aerosol of ether/ethyl acetate after shaking.

A

15 to 30 seconds

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27
Q

The current recommendation is centrifugation at (?) for a minimum of (?).

A

500 g

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28
Q

Let the centrifuge reach the recommended speed before you begin to monitor centrifugation time. If the centrifugation time at the proper speed is reduced, some organisms (?) may not be recovered in the sediment.

A

coccidia and microsporidia

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29
Q

Four layers should result:

A

a small amount of sediment (containing the parasites) in the bottom of the tube
a layer of formalin,
a plug of fecal debris on top of the formalin layer
a layer of ether/ethyl acetate at the top

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30
Q

After the plug of debris is rimmed with an applicator stick, properly decant the supernatant fluid by completely inverting the tube with a single movement and the fluid is allowed to drain for at least (?).

A

5 seconds

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31
Q

(?)

This is particularly important so as not to disturb the sediment. When working with plastic centrifuge tubes, while the tube is still upside down, the sides of the tube is swabbed with a (?) stick to remove excess ether/ethyl acetate.

A

Do NOT tap the tube.

cotton-tipped applicator

32
Q

in the smear of the sediment prepared for examination, forms bubbles that obscure the material being examined.

A

Excess ethyl acetate

33
Q

After proper decanting, a drop or two of fluid remaining on the side of the tube may run down into the sediment. Mix this fluid with the (?) and transfer, using a Pasteur pipette, a small amount of material to a slide and add a coverslip.

A

sediment

34
Q

If the sediment is still somewhat solid, add a drop or two of (?) to the sediment, mix, and examine.

A

saline

35
Q

As in the direct wet smear, (?) can be added to enhance morphological detail.

A

iodine

36
Q

The formalin-ether or formalin-ethyl acetate technique has the following advantages:

A
  1. Easy to perform, allows recovery of the broadest range of organisms - helminth eggs and larvae, and protozoan cysts, and is least subject to technical error.
  2. Sediments can be stored for a long period of time.
  3. Extracts and dissolves fats or mucoidal materials.
37
Q

Similar with other parasitologic methods, this technique also consists of limitations which are follows:

A
  1. Use of ether which is an explosive and flammable compound.
  2. The resulting preparation contains more debris.
  3. Protozoan trophozoites are less likely to be seen.
38
Q

is also based on differences in specific gravity between the sample debris, which in this case is heavy and sinks to the bottom of the test tube, and potential parasites, which are lighter and float toward the top of the tube.

A

zinc sulfate flotation technique

39
Q

In this procedure, zinc sulfate, with a specific gravity of (?) to (?), is used as the concentrating solution.

A

1.18 (for fresh stool)
1.20 (formalin-fixed stool)

40
Q

is added to the stool specimen and centrifuged, the parasites float to the surface and can be skimmed from the top of the tube.

A

zinc sulfate

41
Q

A half-teaspoon of fresh stool is used to prepare an emulsion in distilled water (about 10 ml). Too much or too little specimen will result in an ineffective concentration.

A

distilled water (about 10 ml).

42
Q

However, the addition of fresh stool to distilled water will cause (?) present to rupture.

A

Blastocystis hominis

43
Q

Hence, (?) may substitute for water.

A

0.85% NaCl or 5-10% formalin

44
Q

Some prefer to use (?) for all the rinses throughout the procedure.

A

10% formalin

45
Q

Mix the stool and formalin thoroughly. Let the mixture stand a minimum of (?) for fixation

A

30 minutes

46
Q

A longer centrifugation time (?) for the wash steps are necessary for the possible recovery of coccidia or microsporidia.

A

(10 minutes at 500 g)

47
Q

The washing phase is carried until the supernatant fluid after the centrifugation is (?). Three washings and centrifugations are usually sufficient.

A

light tan or clear

48
Q

If fresh stool is used (or those fixed with non-formalin preservatives), the zinc sulfate should be prepared with a specific gravity of

A

1.180

49
Q

zinc sulfate with specific gravity of (?) is used for formalin-preserved stool.

A

1.200

50
Q

Prepare zinc sulfate ((?) aqueous solution).

A

33%

51
Q

Check the specific gravity of the zinc sulfate using a hydrometer (with a range that includes [?])

A

1.180 to 1.200

52
Q

Using the hydrometer (with the solution at room temperature):

A

•Mix the solution well.
•Float the hydrometer in the solution, giving it a slight twist to see that it is completely free from the sides of the container.
•Read the bottom meniscus.
•Then, adjust to the desired specific gravity (1.180 or 1.200) by adding more zinc sulfate crystals to the solution if below the desired specific gravity ; OR diluting with distilled water the specific gravity is higher than desired.

53
Q

After addition of zinc sulfate, centrifuge for (?). Allow the centrifuge to come to a stop without interference or vibration.

A

1 minute at 500 g

54
Q

Remove the tubes from the centrifuge prior to sampling the (?). This is acceptable; however, there is more chance that the surface film will be disturbed prior to sampling.

A

surface film

55
Q

Two layers should result:

A

a small amount of sediment in the bottom of the tube and a layer of zinc sulfate

56
Q

Remove 1 or 2 drops of the (?) with a freshly flamed (and allowed to cool) wire loop and place them on a slide.

A

surface film

57
Q

Do not use the loop as a (?); simply touch the surface (bend the loop portion of the wire 90o so the loop is parallel with the surface of the fluid).

A

“dipper”

58
Q

Make sure the wire loop is not below the (?). A Pasteur pipette may be used instead of wire loop.

A

surface film

59
Q

Altenative procedure:

A

•Add a small amount of zinc sulfate to the tube so that the fluid forms a slightly convex meniscus.
•A coverslip is then placed on top of the tube so that the undersurface touches the meniscus.
•Leave undisturbed for 5 minutes. Carefully remove the coverslip, and place it on a slide for examination

60
Q

Remove the surface film for examination within (?) of the time the centrifuge comes to a stop.

A

5 minutes

61
Q

Parasites are subject to collapse and distortion when left in contact with (?) for a longer time.

A

high-specific-gravity zinc sulfate

62
Q

If zinc sulfate is the only concentration method used, examine both the (?) to ensure detection of all possible organisms.

A

surface film and the sediment

63
Q

The (?) is advantageous in that it yields a clear preparation than does the sedimentation technique.

A

zinc sulfate floatation technique

64
Q

Similar with the first concentration method, this technique also consists of limitations which are follows:

A
  1. Protozoan cysts and thin-shelled helminth eggs are subject to collapse and distortion.
  2. Some helminth eggs (operculated eggs, or unfertilized Ascaris eggs) do not concentrate well.
  3. Cannot be used for fatty stool, or too hard stool.
65
Q

High specific gravity of the zinc sulfate causes the (?) to pop open; the eggs fill w/ fluid and sink to the bottom rather than float.

A

opercula

66
Q

Unfertilized eggs of (?) are very dense, thus they sink to the bottom of the solution.

A

Ascaris lumbricoides

67
Q

Primarily, a stool concentration technique is indicated when:

A

a. direct wet mount examination of stool samples are negative.

68
Q
  1. Which of the following statements correctly describes a sedimentation technique?
A

A. Stool specimen is suspended in water or normal saline solution.

69
Q
  1. This reagent is used as extractor of debris and fat from the stool to be examined after concentration.
A

C. Ether

70
Q
  1. In the formalin-ether sedimentation concentration technique, appropriate fixation of parasites, if present, is achieved after addition of ether for:
A

A. 10 up to 30 seconds

71
Q
  1. For purposes of safety, ether in the formalin-ether sedimentation concentration technique is widely substituted with:
A

B. ethyl acetate

72
Q
  1. Centrifugation of set ups for formalin-ether sedimentation concentration technique should be carried out for 10 minutes at the speed of:
A

C. 500 g

73
Q
  1. In the ZnSO4 flotation concentration technique, washing phase is carried out until:
A

B. the supernatant is clear

74
Q
  1. The specific gravity of ZnSO4 to be used when formalin-preserved stools are to be subjected to flotation concentration technique is:
A

D. 1. 200

75
Q
  1. Which instrument is used to measure specific gravity of solutions?
A

C. Hydrometer

76
Q
  1. If specific gravity of the ZnSO4 is greater than desired, in order to come up with the desired specific gravity of ZnSO4, adjustment is made by addition of:
A

A. distilled water

Parasitology [LAB] (15 decks)

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