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UND 363 Mwave MSN
UND 363 Mwave Methenamine Silver Nitrate
| Question | Answer |
|---|---|
| purpose for Mwave Methenamine Silver Nitrate | rapid diagnosis of P jirovecii and pneumocystis corinii on cytospin preps or F/S's |
| Principle for Mwave Methenamine 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 | cytospin preps fixes in 95% alcohol, FS fixed in 37-40% formaldehyde, standard paraffin sections with NBF |
| microns | FS - 6 micron, paraffin - 4-5, **sections tend to wash off with this stain so charged slides should be used (poly l lysine or silanized slides) |
| QC | use a control with the fungus you are looking for. chem. cleaned glassware and nonmetal forceps needed |
| reagents in order | 10% chromic acid - oxidizer, soduim bisulfite 1% - remove chromic acid/clearing agent, methenimine silver - impregnation, gold chloride - toner, soduim thiosulfate - remove unreduced silver, lt green -counterstain |
| results | fungi and P jirovecii cell wall - black, background - Green |
| how should the plastic coplin jars be used in the Mwave | put the plastic jars in closed plastic bags, open microwaved bags under fume hood OR put mwave under fume hood |
| if slides are left too long in methenamine silver what will occur | reticular fibers, RBCs and other tissue may be stained. The non specific staining may mimic fungi or obscure small fungi leading to potential false positives. |
| What is mirroring, what can cause it, FIX it? | random deposits of silver onto slides. caused by over heating or dirty glassware. FIX - don't overheat, use ammoniacal silver for impregnation. |