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 _______________________________________________ Histonet mailing list Histonet@lists.utsouthwestern.edu http://lists.utsouthwestern.edu/mailman/listinfo/histonet