Optimization of Silver Staining in Artificial Cytology Samples of Filamentous Fungi

The diagnosis of respiratory fungal infections is often aided by cytopathological evidence of fungi in sputum or bronchoalveolar lavage fluid. Grocott's methenamine silver (GMS) stain, a special stain frequently used to detect fungi in cytological specimens, can be challenging to apply stably. There is a need for improved documentation of staining procedures for fungal detection in cytological specimens. In our study, we developed an artificial cytology specimen for fungal detection by combining cultured fungi with artificial sputum. We compared the conventional GMS protocol with the periodic acid-ammoniacal silver (PAAS) protocol, which our institute uses for cytological samples. Our findings revealed that the PAAS protocol, while showing comparable staining properties to the GMS protocol, resulted in fewer non-specific silver granules in the background. Therefore, we conclude that the PAAS protocol offers a valuable alternative for identifying fungi in cytological specimens.