Microbiology Laboratory


Written by MicroDok

AIM: To concentrate parasites, their eggs, and cysts found in feacal specimens as an aid in the diagnosis of parasitic infections.

PRINCIPLE: The principle of floatation technique of feacal sample concentration is based on the use of saturated sodium chloride solution which has a specific gravity (relative density) that is higher than that of the parasites, their cysts, and eggs; thus allowing them to float to the surface of the brine solution after been emulsified with it and left to stand undisturbed for a given time period.

MATERIALS/APPARATUS: Stool specimen, saturated sodium chloride solution, glass slide, cover slip, test tube, applicator stick, binocular microscope, bulb pipette, test tube rack, timer.


  1. Fill a clean test tube standing on a test tube rack about half filled with the saturated sodium chloride solution.
  2. Collect a good portion of the stool specimen using the applicator stick and emulsify/mix it with the saturated sodium chloride solution in the half filled test tube.
  3. Fill the test tube to the brim with the saturated sodium chloride solution using the bulb pipette.
  4. Carefully place a clean cover slip on top of the test tube. Avoid trapping air bubbles as you do this.
  5. Allow the test tube to stand undisturbed on the test tube rack for about 15 minutes. NOTE: This time is to allow the parasites, their cysts, and eggs to float to the surface of the saturated sodium chloride solution so that they can be properly harvested.
  6. Carefully lift/pull the cover slip straight upwards.
  7. Place the cover slip downwards on a clean glass slide.
  8. Examine the glass slide using the ×10 objective lens and ×40 objective lens of the binocular microscope.

Note:  The condenser iris of the microscope should be closed sufficiently before viewing in order to get a very good contrast. Also, always make sure that you examine several fields of the slide before making your final report, so as to clear all doubts.


Count the number of parasites found and report by their name. Also, the cysts, eggs, WBC, and RBC found are reported as well and if none of these is discovered during the examination, they are reported as “nil”.

It is noteworthy that floatation technique is one of the types of concentration technique which is used to concentrate feacal specimens in the clinical microbiology laboratory. The other concentration techniques are: sedimentation technique, formol ether concentration technique, and zinc sulphate concentration technique.

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