Microscopic Stool Analysis

Stools Analysis - Part 2

Microscopic Examination

• Microscopic analysis of stool specimens includes examining the sample for leukocytes, epithelial cells, blood, qualitative fat, and parasites (eggs, larvae, cysts).
• A large number of leukocytes (> 50 cells per high power field) along with macrophages and erythrocytes are typical of shigellosis.
• A smaller number of pus cells (< 20 per high power field) are found in salmonellosis, and in infections caused by invasive E. coli.
• Few leukocytes (< 5 cells per high power field) are present in cholera, EPEC, and ETEC and viral Diarrhea.
• Large numbers of epithelial cells or large amounts of mucus indicate that the intestinal mucosa is scratched.

Epithelial cells

• Normally, small to moderate numbers of epithelial cells are present in feces.
• The laboratory diagnosis of most parasitic infections is by demonstrating the ova of the parasite in the infected person's stools.

Stool Examination

• Techniques used to examine the stool include saline wet mount examination, iodine preparation, and buffered methylene blue stain.
• Saline wet mount is used for the detection of parasitic trophozoites and cysts of protozoa, and eggs and larvae of helminths.
• Iodine staining method is used to detect cysts of protozoa, but it kills the motile trophozoites.

Stool Testing

Concentration Methods

• Sedimentation is used for detecting Ascaris lumbricoides and Schistosoma mansoni.
• Floatation is used for detecting Enterobius vermicularis and Ankylostoma.

Chemical Testing of Stool

• pH: Normal stool pH is 6-7.5, acidic in amoebic dysentery, and alkaline in bacillary dysentery.
• Occult Blood: May be present in a variety of conditions, including malignancy of the gastrointestinal tract.
• Benzidine test: Used to detect occult blood in the stool sample.

Reducing Factors

• Levels of mono and disaccharide in stool (6mg/g) can indicate disturbances in enzymes that digest sugar.

Stool Culturing

• Stool cultures are undertaken to evaluate diarrhea of unknown etiology to identify possible causative bacteria.
• Bacteria produce diarrhea in three main ways:
  • Organisms invade the intestinal wall, damaging tissue.
  • Organisms produce toxins within the intestine that alter gastrointestinal motility.
  • Toxins produced by bacteria are ingested and produce diarrhea, although the organisms themselves are not detected in feces.

Culture Media

• MacConkey's Agar: Inhibits most gram-positive organisms, differentiating between lactose fermenters and non-lactose fermenters.
• Xylose Lysine Deoxycholate (XLD) Agar: Used for the isolation of Salmonella and particularly Shigella from fecal samples.
• Thiosulphate Citrate Bile Salt Sucrose (TCBS) Agar: Excellent selective medium for the primary isolation of Cholerae.
• Sorbitol MacConkey's Agar: Used for screening E. coli O157.

This quiz covers the microscopic examination of stool specimens, including the identification of various cells, fat, and parasites in stool samples. It also discusses the characteristics of stool samples in shigellosis and salmonellosis.