What is the best fix for protozoa parasites with formalin 10% or 70% alcohol?
Influence of prolonged formalin fixation of tissue samples on the sensitivity of chromogenic in situ hybridization.
Mostegl MM et al. J Vet Diagn Invest. 2011 Nov;23(6):1212-6
https://www.cdc.gov/dpdx/.../stool/specimencoll.html
Comparative studies of the detection rates of Leishmania parasites from formalin, ethanol-fixed, frozen human skin specimens by polymerase chain reaction and Southern blotting.
Uezato H et al. J Dermatol. 1998 Oct;25(10):623-31
If you want to preserve the parasitic morphology in samples such as fecal, 10% formalin is best. If it is for later extraction of DNA or preserve in tissues, better in alcohol
It depends.. if you want to do microscopic studie slater, u can try different fixatives.. Lugol's Iodine..or formaldehyde
Yes, for DNA, then ethanol will be the best choice
check this link: https://aem.asm.org/content/74/8/2505
Some researchers consider ethanol to be a preservative (including myself) rather than a fixative the latter altering the structure of molecules almost irreversibly. If wishing to do molecular studies (i.e., DNA, RNA) ethanol is mandatory as a preservative and material should be transferred from 70% ethanol to absolute ethanol after a short time period. However, if morphological investigations (e.g. histology, whole mount preparations) are to be conducted fix material in 5% formalin (i.e., ~ 2% formaldehyde) buffered to pH 7.2 to 7.4 with sodium hydroxide (phosphate buffers can cause a precipitate with certain fixatives such as Bouin-Hollande). Material kept in 10% formalin (~ 4% formaldehyde) for long term storage can harden and become brittle for optimal histological results and whole mount preparations. Thus, after a brief period in 10% it's advisable to change to 5% formalin for long-term storage. Do not change to 70% ethanol for long-term storage as proteins appear to alter if not break down in ethanol over long term storage.
My experience has been that after a period of time material kept in ethanol for several or more years will not respond well to histological stains such as Mallory's or Heidenhain's triple stains (or even Hematoxylin) or to routine whole mount stains such as Acetic Acid Alum Carmine.
One suggestion I have heard is that if ethanol were indeed a fixative that altered molecular structure, then humans that are heavy consumers of alcoholic beverages would have some of their organs altered irreversibly and that includes the brain.
I do hope that one finds these comments to be helpful. They are based on over half a century of investigations on helminth parasites.
If your intention is to perform DNA extraction, 70% ethanol is best. 10% formalin is best for parasite identification under microscope.
I think Merthiolate stain is more suitable for preserving the stool specimen containing protozoan parasites, Also others such as PVA and SFA solutions. For a short time 70% of alcohol + few drops of glycerin also beneficial.
Formalin can cause shrinkage of the preserved protozoan parasite with time standing.While 70% of ethanol alcohol+ some milliliters of glycerol may be beneficial.For good preservation of protozoan parasite particularly the stool samples;2.5% of potassium dichromate is a good preservative for all cysts and had role in hatching or sporulation of Cyclospora cayetanensis oocysts. Thanks.
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