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UND 363 Grocot silvr

UND 363 Grocott Methanimine Silver Nitrate

QuestionAnswer
purpose for Grocott Methanimine Silver (GMS) Nitrate demo fungus
principle for Grocott Methanimine Silver Nitrate Fungal cell wall polysaccharides are oxidized to aldehydes by chromic acid. Cell walls/glycogen/mucins with large % polysacc.'s will remain reactive to methenimine-silver and reduced to visible.
fix for Grocott Methanimine Silver Nitrate NBF, bouins OK
microns 4-5 or 6 if F/S
QC section with fungus, must use chemically clean glassware and non metallic forceps
reagents in order for Grocott Methanimine Silver Nitrate Chromic Acid 4% - oxidizer, sodium bisulfate 0 removes residual chromic acid, methenamine-silver nitrate - silver impregnation, gold chloride - tone, sodium thio. - remove unreduced silver, lt. green - counterstain
results fungus - black w/ good dilineation, mucin - taupe to dk gray, background - green
what is soduim borate for in the the working methenamine silver nitrate soln' it is used as a buffer
if alcohol is not adequately removed during deparaffinazation and hydration what will happen to the chromic acid there will be a reduction of the chromic acid solution and will cause the color of the soln' to change from orange to brown (DISCARD if the color change is noted)
if the suspected organism is not know what control should be used pneumocystis carinii (it will take longer to stain though)
what should be used for this technique between an oven and a water bath (and why) water bath. it takes 20 min. to reach ambient temperature, whereas an oven will take 1.5 hr to reach ambient in a 60○C oven
what will happen if the silver is overheated it will lead to non-specific staining
what can this stain also demonstrate nocardia asteroides, actinomyces and others
what will occur if periodic acid is used instead of chromic acid (even if it is a trend due to the toxicity of chromic acid) creates false negatives
sections staines with other methods can be stained with G.M.S why? the chromic acid will remove the previous stain
what is the methenamine mix make of? how? and why? mixed just before use, using equal parts soln' 1 (2.1 g silver nitrate/ltr) and sol'n 2 (27g methenamine and 3.7 g borax/ltr) The stock soln's are more stable, contain less silver and cause less nonspecific impregnation
why should gluteraldehyde be avoided the free aldehyde can reduce the silver and give non specific staining.
what will happen to methenamine silver at high temps (above the ideal 40-50○C) it will decompose and will create formaldehyde which will recuce silver nonselectively on tissue/the container/and the solution.
what will the microscope show if it has been over stained the morphology of the fungi will be obscured and ID will be difficult
Created by: mustangvxd
 

 



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