One of the pathologists I worked for would insist that we also perform a
Gridley's Stain  for Fungus along with the GMS for this very reason.  We at one
time routinely used periodic acid but during a re-evaluation, I switched back to
chromic acid.  We used a 10% Chromic Acid solution because it oxidized quicker.
Pneumocystic stains very well using periodic acid, it was the other types of
fungus I was concerned about.

There was a very interesting article written in the JOH in reference to this
very subject.  Unfortunately, I do not have all my editions at work.  It was one
of the more current ones.  Maybe someone reading this can provide the edition
month and number.

Rande Kline, HT (ASCP)
Technical Services
EM Science/BDH




RSRICHMOND@aol.com on 02/10/2000 09:52:35 AM

To:   histonet@pathology.swmed.edu
cc:    (bcc: Rande Kline/EMI/Merck)
Subject:  methenamine silver (GMS) for fungi



Several posts have alluded to a problem I'd like to know the answer to.

The traditional GMS (Gomori or Grocott methenamine silver) stain for fungi
(including Pneumocystis carinii, which alternates weekly between being a
fungus and a protozoan) uses chromic acid as an oxidizing agent, to cleave
vicinal diol linkages and thus produce aldehyde groups which then reduce an
ammoniacal silver reagent (methenamine silver).

Chromic acid, a very strong oxidizing agent, is used because it produces
aldehyde groups in very resistant fungal cell walls.

Because of its environmental problems, chromic acid has become difficult to
use. Kit manufacturers, with a wave of an MBA's hands I suppose, have
declared that periodic acid, a much weaker oxidizing agent, can be used in
its stead. But where is the literature to support this change?

Different fungi differ greatly in their demonstrability with this technique,
and ideally one would have a different control for every fungus one wished to
demonstrate. Probably the most difficult of common pathogenic fungi is
Histoplasma capsulatum in old fibrotic or caseous lesions.

If I saw a study that found periodic acid to be as good as chromic acid for
this "acid test", then I might believe.

Bob Richmond
Samurai Pathologist
Knoxville TN