[Histonet] Re: Fungus controls

Bob Richmond rsrichmond <@t> gmail.com
Wed Nov 6 12:38:31 CST 2013

I wouldn't be too happy with any of these substitutes for proper fungus
controls. Ideally, your control would be the fungus you're looking for,
obviously not a practical way to do it.

The usual fungus control I see is mouse lung with yeast, presumably
Candida, injected into normal lung tissue. This control will stain very
satisfactorily with PAS, and is not really a good test of the efficacy of a
fungus stain.

The most exacting fungus control for the GMS stain is histoplasma, an old
infection in which some of the yeast cells are actually dead. If you can
stain that, you can stain any fungus you're likely to encounter. Freida
Carson did an elegant study a number of years ago (reference below) of how
critical the oxidation step is in this endeavor.

The decline of medical autopsies has made controls like this much more
difficult to obtain, but when you can get it, you can get large quantities
of it which need to be effectively shared.

Bob Richmond
Samurai Pathologist
Maryville TN
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

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