[Histonet] Re: staining dead fungi

[Bob Richmond]

Jeanine H. Bartlett, BS HT(ASCP), QIHC at the CDC (Go CDC! - difficult
fungus problem this week) in Atlanta asks about staining "dead fungi"
in paraffin-embedded tissue.

The usual problem is Histoplasma capsulatum. Histologically
old-looking granulomas can contain fungus that's resistant to silver
staining.

Obviously the usual stain is GMS, which should use chromic acid as the
strong oxidizing agent to break open and oxidize vicinal diol groups
in fungal cell walls.

Because of the environmental problems attendant on handling chromium,
many commercial GMS kits substitute periodic acid, a much weaker
oxidizing agent. Histoplasma in old granulomas often does not stain.

Freida Carson published a major study of this problem several years ago:

Inconsistent Detection of Histoplasma capsulatum with Periodic Acid
Oxidation in the Grocott Methenamine-Silver Nitrate (GMS) Fungus
Stain. Freida L. Carson, Jerry Fredenburgh, and John E. Maxwell. J
Histotechnol [June] 1999;22:119.

Bob Richmond
Samurai Pathologist
Maryville TN