Microbiology Laboratory


Written by MicroDok

Concentration techniques are used to concentrate the eggs/ova of parasites and the cysts/trophozoites of protozoa in feacal samples especially when they occur in small amounts in the sample being examined. This method does not detect the motile forms of parasites in feacal samples; thus the microscopy of the sample should first be undertaken before carrying out any concentration technique using the same sample. There are three concentration methods available in the Parasitology laboratory:

  1. Sedimentation method: This technique makes use of a filter paper strip to concentrate the larvae of parasites. The filter paper is spread with the feacal specimen and then inserted into a tube containing clean boiled water, sealed with cotton wool and allowed to stand for about 4-6 days. Any larvae present in the feacal specimen will travel against the water current and settle at the bottom of the test tube. The sedimentation concentration method is used to investigate the larvae of parasites such as Strongyloides stercoralis.
  2. Formaldehyde method: This technique is divided into two parts: the formaldehyde-ether sedimentation technique and the formaldehyde-detergent sedimentation technique. Both of these techniques make use of centrifugation and different concentrations of formalin to concentrate the eggs/ova of parasites but the formaldehyde-ether sedimentation technique also adds ether in its methodology. The presence of formaldehyde helps to preserve any parasite which may be present in the feacal specimen.
  3. Floatation method: The floatation concentration technique involves the mixing of the feacal specimen in a saturated solution of sodium chloride. The saturated sodium chloride solution allows the eggs/ova of the parasites in the feacal sample to float to the surface of the solution from where they can be conveniently harvested. Floatation method is appropriate for detection of the eggs of Ancylostoma duodenale, Ascaris lumbricoides, and Taenia

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