[Histonet] Re: Fungal stains

From:"Robert Richmond"

Colin Weaver asks about staining of various fungal species by the
standard fungal stains.

The standard fungal stains have two basic steps:

1. Periodic acid or chromic acid splits bonds between vicinal diol
groups (two carbons with OH"s on adjacent carbon atoms) and oxidizes
the free ends to aldehyde groups (-CHO).

2. The aldehyde groups oxidize Schiff's reagent or methenamine silver
to produce a visible deposit.

Periodic acid is not a sufficiently strong oxidant to demonstrate some
fungal cell walls. In human pathology, Histoplasma is most likely to
stain weakly or not at all. You need chromic acid, most usually
followed by methenamine silver.

Unfortunately, many so-called GMS kits silently substitute periodic
acid for the more hazardous chromic acid. Freida Carson reviewed this
top in J Histotechnol several years ago - I can find the reference if
anyone needs it (I think I've posted it on Histonet before, so it's
probably in the archives.) So your first step is to see if you're
actually using chromic acid.

PLEASE get the politics off this list - the repetitious garbage is
making the list hard to read, particularly in digest form. Linda
Margraf, if it doesn't stop, I suggest moderating the list for a few
days, though not permanently.

Bob Richmond
Samurai Pathologist
Knoxville TN

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