A Comparison of Histological Staining Methods for Pathogenic Fungi in Humans

Abstract

Background: Using special stains to detect fungus is an essential diagnostic tool in histology. Because microbiology cultures can take over a month for a definitive diagnosis, rapid detection and treatment of fungal infections are necessary for patient care, particularly in immunocompromised patients when infections may lead to life-threatening complications. Objective: A comparison of various classic special stain methods along with more recent modifications on those staining methods was performed to evaluate the effectiveness of fungal detection while attempting to ameliorate the dangers associated with certain chemicals used in histochemical procedures. Methods: Twenty-five formalin-fixed paraffin-embedded archived tissue blocks containing the genera <i>Aspergillus, Blastomyces, Candida, Cryptococcus, Histoplasma, Mucor, </i>and <i>Pneumocystis</i> were stained with periodic acid Schiff light green (PAS-LG) and Grocott methenamine silver (GMS) using standard methods. Modifications of these and other protocols found in the literature to include altering the oxidizing reagent, time in oxidizer, temperature of oxidizer, pretreatment, and counterstain applied were made and the results were compared. Results: <i>Cryptococcus</i> and <i>Candida</i> were the most readily labeled fungal genera with detection rates of 92% and 85%, respectively across all staining protocols assayed. <i>Histoplasma</i>, however proved to be the most difficult genus to successfully label with only a 21% sensitivity across all staining protocols. Conclusion: While several procedures which included altering oxidizers, incubation periods, and temperatures were variably successful, the original Grocott method with chromic acid as the oxidizer remained the most effective protocol in the detection of fungal elements with 96% sensitivity.