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UND 363 Grocot silvr
UND 363 Grocott Methanimine Silver Nitrate
| Question | Answer |
|---|---|
| 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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