Stool examination

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: A nkylostoma duodenale H ymenolepis nana E nterobius N ecator americans

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

15. Cyst:- infec tive 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. UN FERTILED 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. A nkylostoma duodenale N ecator 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.

22. E nterobius vermicularis It is a planoconvex, elongate and an asymmetric egg which meas ures 55 x 26 µ. Its shell is thin and smooth. Fully developed larvae are seen in the eggs.

23. 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