Fecal Examination Using the Zinc Sulfate Centrifugal Flotation Method
Below is a description of how to test fecal samples using the Zinc Sulfate Centrifugal Flotation Method:
- Fill a 15 ml centrifuge tube with ZnSO4 solution (1.18 specific gravity)* and pour into a glass dish.
- Using a tongue depressor, push the feces (2 to 3 grams - about 1 cm in diameter) through a strainer into the ZnSO4 solution in the dish.
- Using a funnel, pour the ZnSO4-fecal mixture back into the centrifuge tube.
- Centrifuge for 2 minutes at high speed (1500 - 2000 rpm).
- Using a headed-rod or loop, remove a sample from the surface of the solution and place on a microscope slide. You may have to take several samples with the rod or loop to get enough material to examine - you want the equivalent of a large drop on the slide. Add a drop of iodine (to stain the cysts and the ova) and a coverslip. Examine at 10X on a microscope.
Note: If the sample contains a large amount of fat or other material that floats in water, you may want to wash the sample before doing the flotation. To do this, start at step 1 but use water instead of ZnSO4. When you centrifuge the water-fecal mixture, the eggs will sink but the fat will remain afloat as the eggs are heavier than water. After centrifugation pour off the supernatant and add the ZnSO4 solution - mix well. Centrifuge as in step 5.
* ZnSO4 solution (1.18 specific gravity) is made by adding 386 grams of ZnSO4 to 1 liter of water. The mixture should be checked with a hydrometer and adjusted to 1.18 specific gravity.. The ZnSO4 solution should be stored tightly capped to prevent evaporation (and the resulting change in specific gravity of the solution).
