Grocott's Methenamine Silver
Classification: microorganism stain
Purpose: stain fungi
Mechanism of staining: induced argentaffin metallic impregnation
Positive controls: any tissue containing fungi
Grocott's Methenamine Silver
Protozoa in lung
REAGENT | PURPOSE | MECHANISM OF STAINING | SOURCE OF ERROR |
Chromic acid | Oxidization | Strong oxidizer that over-oxidizing all tissues, creating reactive aldehyde groups in fungi | Omitted: No aldehyde groups will be produced and no fungi demonstrated. |
Too short: Background staining. | |||
Too long: Over oxidation of aldehyde groups and no demonstration of fungi. | |||
Sodium bisulphite | Bleaching | Removes brown discoloration created by the chromic acid | Omitted: Discoloration in counterstain |
Too short: No effect. | |||
Too long: No effect. | |||
Methenamine silver (preheated to 60 Celsius) | Impregnation | Silver binds with the aldehyde groups. Aldehydes reduce silver to visible black color. | Omitted: Fungi will not be demonstrated. |
Too short: Patchy staining of fungi may be seen. | |||
Too long: Dark fungi that obscure details necessary to differentiate species (septae) | |||
Gold chloride | Toning | Substitute silver with gold by ion exchange Removes any brown color in other tissue components | Omitted: Collagen will remain golden brown. |
Too long: Production of red tones due to overtoning. Will start to remove silver staining. | |||
Too short: No effects on the staining. | |||
Sodium thiosulphate | Fixation | Removes unreacted silver | Omitted: Causes non-specific blackening of tissue over time. |
Too long: No effects on the staining. | |||
Too short: Causes blackening of tissue over time. | |||
Light green or Neutral red | Counterstain | | Omitted: No other tissue components demonstrated. |
Too long: Fungi obscured. | |||
Too short: Other tissues stain lightly and no detail seen. |
Well Stained Slide
Fungi: black outline with grey interior
Lung: green
Fungi: black-brown
Possilby over-toned
Special Considerations
No metal forceps should be used when working with this stain.
References
Officer B. HIML251 Lecture notes: Silver Stains: Grocott’s Methenamine Silver, Jone’s Methenamine Silver, and Masson Fontana, March 18, 2009