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Laboratory Procedures for Identifying Parasitic Organisms and Their Ova 267

flotation procedure but it should be noted that the flotation method is not particularly
effective in the recovery of operculated eggs and unfertilized Ascaris lumbricoides
ova. And with iodine, the zinc sulfate kills trophozoites and alters the morphology of
some fragile eggs such as those of Hymenolepsis nana. If these organisms are sug-
gested from history and from the wet mount, the formalin-ethyl acetate sedimentation
method should be utilized.

Equipment and Supplies
1. Protective gloves and disposable gown
2. Clean water (deionized or distilled water may be preferable to avoid contaminants)
3. 13 3 100 round-bottom test tubes
4. Fixed and washed fecal sample obtained by the following steps.
5. Centrifuge with head adaptable for the 13 3 100 test tubes
6. 22 3 22 mm cover glasses
7. Test tube rack configured to hold tubes in vertical position

8. Pasteur pipettes
9. Microbiological wire loop
10. Standard microscope slides

11. Zinc sulfate of 1.20 specific gravity
12. Saline for washing samples

Clinical Precaution:
Specific gravity of zinc sulfate should be verified by use of a hydrometer.

A specific of 1.20 is preferable for formalin-preserved specimens.

Procedural Steps
33% Zinc Sulfate Solution Preparation
330 g zinc sulfate
Water added to reach (QS) a volume of 1000 mL

Additional water or zinc sulfate to produce a specific gravity (SpG) of 1.18. Specifi c
gravity can be determined with a hydrometer and adjusted to 1.20 by adding small

amounts of zinc sulfate. Zinc sulfate centrifugal flotation has the unique ability to fl oat
Giardia cysts as well as other parasite structures. It is a simple, accurate, and inex-
pensive procedure that can be performed in almost any basic clinical laboratory.

1. Prepare washed and fixed fecal sample in a 13 3 100 mm test tube. The sample
is prepared by centrifuging the suspension at 1500 rpm for 10 minutes and then
carefully pouring off the supernatant into a container containing disinfectant.
If the sample still contains a large amount of fecal debris, resuspend the sample
in 10 to 15 mL of saline or formalin and recentrifuge. This procedure may be
repeated in the presence of excess fecal debris.
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