[Histonet] Re: GMS better than PAS for fungi

[Bob Richmond]

Freida Carson wrote what was probably the definitive study of the subject
about 15 years ago.

What stain you need depends on what fungus you're trying to stain. PAS does
fine for Candida. The most critical test of a fungal stain is its ability
to stain old ("obsolete") Histoplasma.

Here's the abstract of her article:

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
1. Department of Pathology, Baylor University Medical Center
2. Richard-Allan Scientific Kalamazoo MI
3. Glenwood Regional Medical Center, West Monroe LA

J Histotechnol [June] 1999;22:119

Abstract

Grocott's modification of the Gomori methenamine silver staining technique
is widely recognized as the best method for the detection of fungal
elements in tissues. Although chromic acid remains the preferred oxidizing
agent in many laboratories, in recent years there has been a trend toward
replacing it with periodic acid because of safety, stability, and
environmental issues. Our experience indicated that 1% periodic acid
oxidation for 5 to 30 min at room temperature is insufficient for
consistent detection of H. capsulatum, although adequate staining of
Aspergillus sp. is obtained. Consequently, false-negative results may be
reported. We recommend that the period of oxidation with periodic acid
should be extended to 1 hr at 56 to 60°C to ensure consistent demonstration
of H. capsulatum. These observations also underscore the importance of the
use of matched positive controls when analyzing fungal stains. (The J
Histotechnol 22:119-122, 1999)

Bob Richmond
Samurai Pathologist
Maryville TN