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Questions and Answers
What is the primary purpose of conducting stool cultures?
What is the primary purpose of conducting stool cultures?
Which method by which bacteria produce diarrhea involves damaging the intestinal wall?
Which method by which bacteria produce diarrhea involves damaging the intestinal wall?
Which culture medium is recommended for isolating Salmonella and Shigella?
Which culture medium is recommended for isolating Salmonella and Shigella?
What does MacConkys Agar differentiate between?
What does MacConkys Agar differentiate between?
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Which bacteria produces colorless colonies on Sorbitol MacConkys agar?
Which bacteria produces colorless colonies on Sorbitol MacConkys agar?
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Which selective medium is used for the primary isolation of Cholerae?
Which selective medium is used for the primary isolation of Cholerae?
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What technique is used to detect live motile trophozoites of protozoans?
What technique is used to detect live motile trophozoites of protozoans?
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Which solution is used in the saline wet mount method?
Which solution is used in the saline wet mount method?
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What is buffered methylene blue stain used for?
What is buffered methylene blue stain used for?
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Which concentration technique is used for detecting Ascaris lumbricoides?
Which concentration technique is used for detecting Ascaris lumbricoides?
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What stool pH is typically observed in bacillary dysentery?
What stool pH is typically observed in bacillary dysentery?
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Which reagent is used in the occult blood test?
Which reagent is used in the occult blood test?
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Increasing levels of which substances indicate disturbances in sugar digestion enzymes?
Increasing levels of which substances indicate disturbances in sugar digestion enzymes?
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Which of the following is a disadvantage of iodine staining method?
Which of the following is a disadvantage of iodine staining method?
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Which of the following parasites can be detected using flotation concentration technique?
Which of the following parasites can be detected using flotation concentration technique?
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What color indicates the presence of occult blood in the stool sample?
What color indicates the presence of occult blood in the stool sample?
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Study Notes
Stool Culturing
- Stool cultures are used to evaluate diarrhea of unknown etiology to identify possible causative bacteria.
- Bacteria produce diarrhea in three main ways:
- Invading the intestinal wall and damaging tissue
- Producing toxins that alter gastrointestinal motility
- Producing toxins that are ingested and cause diarrhea, even if the organisms are not detected in feces
Culture Media
- MacConkys Agar: inhibits most gram-positive organisms, differentiating between lactose fermenters and non-lactose fermenters
- Xylose Lysine Deoxycholate (XLD) Agar: selective medium for isolating Salmonella and Shigella from fecal samples
- Thiosulphate Citrate Bile Salt Sucrose (TCBS) Agar: excellent, selective medium for primary isolation of Cholerae
- Sorbitol MacConkys Agar: used for screening E. coli 0157, which produces colorless colonies on this medium
Laboratory Diagnosis of Parasitic Infections
- Stool ova and parasites test is used to diagnose most parasitic infections
- Techniques used to examine the stool include:
- Saline wet mount examination and iodine preparation
- Concentration techniques
- Buffered methylene blue stain
Stool Examination
- Saline wet mount is used to detect live motile trophozoites, cysts, eggs, and larvae in stool
- Iodine staining method is used to detect nuclei of some cyst forms of protozoans, but it kills motile trophozoites
- Buffered methylene blue stain is used for nuclear stain in Entamoeba histolytica
Concentration Methods
- Sedimentation is used for detecting Ascaris lumbricoides and Schistosoma mansoni
- Flotation is used for detecting Enterobius vermicularis and Ancylostoma
Chemical Testing of Stool
- pH: normal stool pH is 6-7.5, acidic in amoebic dysentery, and alkaline in bacillary dysentery
- Occult blood test: used to detect occult blood in stool, which may indicate malignancy or other conditions
- Reducing factors: used to detect disturbances in enzymes that digest sugars, such as lactase and sucrase
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Description
This quiz covers the importance of stool cultures in identifying causative bacteria of diarrhea and the mechanisms of bacterial diarrhea. It explores the normal flora of the bowel and how pathological bacteria can cause infection.
