Stool examination mbbs 2 Microbiology

1. Examination of Feces
▰ As many parasites inhabit in the intestinal tract, stool examination is the
most common diagnostic technique used for the diagnosis of parasitic
infections.

2. Specimen Collection
▰ Stool specimens should be collected
in a wide-mouthed, clean, leak-proof,
screw capped containers and should
be handled carefully to avoid
acquiring infection from organisms
present in stool.

3. If delay in transport:
▰ Fecal specimens should be kept at room temperature;
▰ Preservatives (e.g. 10% formalin) - used to maintain the morphology of the
parasitic cysts and eggs.

4. Timing:
▰ Collected before starting anti-parasitic drugs and closer to the onset of
symptoms.
Frequency:
▰ At least three stool specimens collected on alternate days (within 10 days).

5. When to examine:
▰ Liquid stool specimens - examined within 30 minutes,
▰ Semisolid stools - within 1hr.
▰ Formed stools - up to 24 hours after collection.

6. Macroscopic Examination
▰ Mucoid bloody stool: acute amoebic dysentery & intestinal
schistosomiasis.
▰ Color: Dark red stool - upper gastrointestinal tract (GIT) bleeding and a
bright red stool - bleeding from lower GIT.
▰ Frothy pale offensive stool (containing fat) - found in giardiasis.

7. Stool Consistency
▰ In liquid stool - trophozoites are usually
found.
▰ Semi-formed stool - both trophozoites and
cysts are found.
▰ Formed stool - cysts are mainly found.

8. Microscopic Examination
▰ Includes direct wet mount examination
▰ Permanent staining methods.

9. Direct Wet Mount (Saline and Iodine
Mount)
▰ Drops of saline and Lugol’s iodine
are placed on left and right halves
of the slide respectively.
▰ A small amount of feces (~2 mg) -
mixed with a stick to form a
uniform smooth suspension.

10. ▰ Cover slip - placed on the mount and
examined under low power objective
(10X) for detection of helminths eggs
and larvae; followed by high power
objective (40X) for protozoan cysts
and trophozoites.
Method of screening of slide

11. Saline Mount
▰ Useful in the detection of trophozoites and cysts of protozoa, and eggs
and larvae of helminths.
▰ Advantages than iodine mount:
 Motility of trophozoites and larvae in acute infection.
 Bile staining property can be appreciated - bile stained eggs appear
golden brown and non-bile stained eggs appear colorless.

12. Iodine Mount
Advantages:
▰ Nuclear details of protozoan cysts, helminthic eggs and larvae are better
visualized, compared to saline mount.
Disadvantages:
▰ Iodine immobilizes and kills the parasites, hence motility of the
trophozoites and helminthic larvae cannot be appreciated
▰ Bile staining property cannot be appreciated.

13. Non-bile stained eggs
▰ Eggs of most of the intestinal parasites when they pass through intestine
are stained by bile.
▰ Exceptions:
 Ankylostoma duodenale
 Hymenolepis nana
 Enterobius
 Necator americans

14. Entamoeba histolytica
Trophozoite
• 12-60 µ, asymmetric,
• single spherical nucleus,
• a single central karyosome

15. Cyst:-
infective stage of the parasite.
Spherical; 10- 20 µ.
mature cyst with four nuclei, with a compact, centrally located karyosome
Entamoeba histolytica

16. Giardia lamblia cyst
 oval
 8-12 µ long and 7-10µ wide,
 nucleus has 4 karyosomes, which tend to
be eccenterically placed.
 There is a clear space between the cell
wall and the cytoplasm.
 median bodies are present

17. Ascaris lumbricoides
Fertile egg
 60 × 45 µ
 round or ovoid with a thick
shell.
 covered by a thick albuminous
coat,
 its inner cell is in various
stages of cleavage.
 brown in colour.

18. • UNFERTILED EGG
• It measures 90x40 µ, it is elongated, its shell is often thin and its internal material is a mass of
globules.
Ascaris lumbricoides

19. Trichuris trichura
• It is elongate and barrel shaped, with polar hyaline plugs. It measures 54-22 µ. Its shells is yellow
to brownish and its plugs are colourless.

20. HOOKWORM
• They are oval and ellipsoid and they measure 60x40 µ. Their shells are thin walled,
smooth and colourless. Their internal cleavages are well developed at the 4-8 cell
stage, which pull away from the shell, leaving an empty space.
• Ankylostoma duodenale
• Necator americans

21. Taenia spp.
• It is spherical, it measures 31-43µ and it has a thick shell with prominent radial striations. An
embryonated oncosphere which possesses 3 pairs of hooklets within the shell is diagnostic of the
genus. Species identification on the basis of morphology is not possible.

23. Enterobius vermicularis
• It is a planoconvex, elongate and an asymmetric egg which measures 55 x 26 µ. Its shell is thin and
smooth. Fully developed larvae are seen in the eggs.

24. Hymenolepis nana (H. nana)
size range of 30 to 50 µm. On the inner membrane are
two poles, from which 4-8 polar filaments spread out