12 Questions
What is the purpose of concentrating feces in a laboratory setting?
To decrease the amount of background material in the preparation
Before conducting fecal concentration techniques, what should be done first?
Perform a direct examination
What does the sedimentation technique rely on to separate parasites from the sample?
Parasites' specific gravity
Why are motile protozoan trophozoites not found in concentrated preparations?
They are removed during the concentration process
Which concentration technique is recommended for the recovery of Trichuris, Capillaria & Schistosoma eggs from animal specimens?
Acid ether concentration technique
What is the clearing agent used in the formalin ethyl acetate concentration technique?
HCl
What is the advantage of using ethyl acetate in the centrifugation technique described?
It removes fecal debris more effectively
What is the main disadvantage of using the zinc sulfate centrifugal flotation technique?
Some parasites may be missed as they do not float
Why is Sheather's flotation technique recommended for concentrating Cryptosporidium oocysts?
Uses sugar solution preserved in phenol
Why is Brine's flotation not suited for recovering Trematode eggs?
The eggs will not float in Brine's solution
What is the main benefit of using zinc sulfate centrifugal flotation over ethyl acetate technique?
Removes more fecal debris
Why would hookworm eggs and Schistosome eggs be badly shrunken in Brine's flotation?
They are too dense to float in Brine's solution
Study Notes
Purpose of Concentrating Feces
- Increase the possibility of finding protozoan cysts, helminth eggs, and larvae by decreasing background material and concentrating organisms.
Importance of Direct Examination
- Should be done before proceeding to fecal concentration, especially for light infections.
Concentration Techniques
- Can be performed on fresh or preserved stool specimens.
- Increase the number of organisms detected compared to direct microscopy.
- Motile protozoan trophozoites are not found in concentrated preparations.
Sedimentation Technique
- Based on principle of specific gravity: parasites settle at the bottom of the tube after centrifugation.
Flotation Techniques
- Parasites float to the surface and can be skimmed from the top of the tube.
Acid Ether Concentration Technique
- Method of choice for specimens from animal sources.
- Recommended for recovering Trichuris, Capillaria, and Schistosoma eggs.
- Uses HCl as a clearing agent and ether to remove fats.
Formalin Ethyl Acetate Technique
- Most widely used sedimentation technique.
- Recommended for recovering Giardia lamblia cysts and cestode eggs.
- Provides good recovery of most parasites and is easy to perform.
Zinc Sulfate Centrifugal Flotation Technique
- Uses zinc sulfate with a specific gravity of 1.18 to 1.20 as the concentrating solution.
- Recommended for recovering Giardia lamblia cysts and H. nana ova.
- Advantage: removes more fecal debris, yielding a cleaner preparation.
- Disadvantage: may miss some helminth eggs due to density.
Sheather's Flotation Technique
- Uses sugar solution preserved in phenol.
- Recommended for concentrating oocysts of Cryptosporidium and Isospora.
Brine's Flotation Technique
- Uses salt solution, with no centrifugation required.
- Procedure is simple, economical, and suited for mass stool examination.
- Not recommended for Trematode eggs as they do not float in brine.
- Hookworm eggs and Schistosome eggs become badly shrunken.
Test your knowledge on fecal concentration techniques used to find protozoan cysts, helminth eggs, and larvae in medical samples. Learn about the importance of concentrating feces and how it increases the chances of detecting organisms compared to direct examination.
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