Saline Wet Mount for Stool: Introduction, Principle, Preparation, Result Interpretation, Limitations and Related Videos

Saline wet mount preparation for stool uses analyzing a stool specimen in coprology (study of feces). It utilizes a physiological saline solution (0.85% NaCl ) as an isotonic media to maintain the cellular structure of the various organisms as well as our cells that are found in stool.

Saline Wet Mount for Stool

Saline wet mount for stool or stool wet mount is the simplest and basic method for study of feces and applicable in every medical laboratory even in small set up. It uses for following purposes-

  1. To observe live  trophozoites ( e.g.  Entamoeba histolytica/dispar, Girdia lablia, Trichomonas, etc.) and larvae of parasites ( e.g. Strongyloides stercoralis) are motile except inactive forms.
  2. To find out egg, cysts, oocysts of different parasites ( Helmiths, protozoa and coccoidian parasites).
  3.  To determine the presence of leukocytes and erythrocytes in a fecal smear.
  4. It also gives clue towards motility of bacteria (Shigella  non-motile causing bacillary dysentery where as Vibrio cholerae shows darting motility which is causative agent cholera).
  5. It also remarks presence of fungal elements ( yeast cells, hyphae or fungal spores).
  6. It also visualizes the presence of non parasitic structures like Charcot Leyden crystal,  muscle fibres, fat globules, starch cell, vegetable fibres, hair, etc.

Principle of saline wet mount of stool

Saline wet mount preparation for stool uses analyzing a stool specimen in coprology (study of feces). It utilizes a physiological saline solution (0.85% NaCl ) as an isotonic media to maintain the cellular structure of the various organisms as well as our cells that are found in stool.

Requirements for saline wet mount

  • Physiological saline ( 0.85% NaCl)
  • Specimen: stool
  • Sterile bamboo sticks or low cone on the end of a wooden applicator stick
  • Clean and grease free slides and
  • Cove slips(22- by 22-mm)
  • Microscope
  • Gloves

Saline wet mount of stool Preparation

  1. First wear the groves.
  2. Take a clean and grease free slide.
  3. Add one drop of physiological saline and then add  a stool equivalent to a match stick head (2 mg)  with the help of  stick.
  4. Mix it properly and apply a cover slip over a uniform suspension  without creating bubbles.
  5. Note: If a fresh stool specimen is received and if blood and mucus are present, the specimen should be examined as a direct mount making sure to sample the bloody areas.
  6. Examine the entire 22- by 22-mm cover slip systematically with the low power objective (10X ) and low light intensity.
  7.  If any suspicious objects encounter, examine with the high dry objective (40X).

Result Interpretation

Presence of active trophozoite/s: Motile retractile bodies

Cyst , oocyst, egg, inactive trophozite/s, larvae: Retractile bodies and finally focus at high dry power field

Key notes

  1. There is a little difference between normal and physiological saline. Physiological saline is  0.85% NaCl where as normal saline 0.9% NaCl.
  2. Gram’s iodine  is not applicable for staining parasitic organisms and for this D’Antoni’s iodine uses.
  3. Oil immersion examination is also preferred in parasitology for the permanent stained smear of parasites.
  4. Intestinal protozoa can not conform on the basis of a wet mount alone and thus permanent stained smears requires to confirm the specific identification of suspected organisms.

Limitations of saline wet mount for stool examination

  1. Due to lack of stain, it is difficult to get morphological details.
  2. Inappropriate preparation of the smear may hide parasites.
  3. Improper adjustment of the microscope in relation to the objective may create problems.

Saline Wet mount Related Videos-

Heavy load of parasites in stool|| Stool microscopic examination|| Trichomonas hominis in saline wet mount of feces as shown below-

Trichuris trichura or whip worm under saline wet mount at 40X objective under the microscope –
Features: Barrel shape
Mucus thread at each pole as shown in video

Egg of Taenia species
They are spherical, brown in color (bile stained) and measure 30-40 µm in diameter.
They are surrounded by embryophore which is brown, thick walled and radially striated.
Inside embryophore, hexacanth embryo (oncosphere) present with three pairs of hooklets.
They do not float in saturated solution of common salt (brine solution).
The are  viable for 8 weeks.

Roundworm or Ascaris lumbicoides egg under the microscope in saline preparation
egg-infertile
Finding of eggs
In stool:
direct microscopic examination of a saline emulsion of the stool
Concentration methods may be used.
Note:
Fertilized egg floats in salt solution
Unfertilized eggs do not float

Hymenolypsis (now called Vampirolepsis)  egg in saline wet mount of stool : showing hooklets egg of Hymenolepis liberated in feces by gradual disintegration of terminal segments

Spherical or oval in shape, 30-45 µm

Two distinct membranes

Outer membranes thin and colorless

Inner embryophore encloses an oncosphere with 3 pairs of hooklets

Space between two membrane –filled with yolk granules and polar filaments emanating from little knobs at either end of embryophore.

Egg of hookworm ( Ancylostoma duodenale or Necator americanus)  in saline preparation of stool under the microscope
Egg features-
Shape: oval or elliptical with flattened poles( one pole more often flattened than other), size: 65 X 40 um, color : colorless ( no bile stain), dark brown as stained with iodine. Shell : very thin transparent hyaline shell membrane, appears as black line and contain: segmented ovum with 4 blastomeres, has a clear space between egg shell and segmented ovum. Float in saturated NaCl. Type: A( fresh stool) : 4 ,8, 16 grey granular cell clear blastomeres. Type :B( few hour old): a uniform mass of many grey granular cells. Type: C( 12-48 hr): whole of egg is filled with larva, embryonated.

Enterobious vermicularis ( common manes pinworm or threadworm or seatworm) – eggs and some are with larva in saline wet mount of feces –
Shape : oval, planoconvex.

Size : 50-60μm x 20-30μm.

Surrounded by double layered egg shell

Embryonated when passed fresh; contains a tadpole larva inside.

Entamoeba coli Cyst with 8 nuclei in iodine wet mount as shown below-

Giardia lamblia cysts in iodine wet mount as shown below ( look at center)-

Entamoeba histolytica (Amoeba) trophozoites and cyst in LPCB preparation as shown below-

Blastocystis hominis cyst in Sargeaunt stained slide under the microscope  as shown below-

Oocyst of Cyclospora cayetanensis ( coccidian parasite) in saline wet mount of stool under the microscope as shown below-

References

  1. Medical Parasitology by Abhay R. Satoskar, Gary L. Simon, Peter J. Hotez and Moriya Tsuji
  2. Atlas of Medical Helminthology and ptotozoology -4th edn  -P.L.  Chiodini, A.H. Moody, D.W. Manser
  3. Merkell and voge’s medical parasitology
    9th edition.
  4. Parasitology: 12th edition
    By K. D. Chatterjee
  5. District laboratory practice in Tropical countries –Part-I .
    By Monica cheesbrough.
  6. Isenberg clinical microbiology procedures Handbook
    2nd edition. Vol. 2
  7. http://www.med-chem.com/para-site.php
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