A practical protocol for the identification of Schizophyllum commune in fungal cultures of respiratory specimens: A pilot study at a single center in Japan.

BACKGROUND: Although Schizophyllum commune is a common causative fungus of allergic bronchopulmonary mycosis, it is often underrecognized in clinical practice. This is because it rarely forms spores under routine culture conditions, typically appears as white, non-sporulating colonies indistinguishable from other fungi, and is frequently dismissed as a contaminant rather than subjected to molecular identification. To minimize the risk of being overlooked, we established a practical protocol for the identification of S. commune based on its ability to produce hydrogen sulfide.

METHODS: To evaluate the clinical utility of this protocol, we studied consecutive lower respiratory tract specimens collected for fungal culture from adult patients who visited a tertiary hospital for allergy and respirology. Fungal cultures were performed in accordance with this protocol between January 2023 and December 2024. We calculated the positive and negative predictive value of this protocol as a clinical test for identifying S. commune by detecting genetic analysis-proven S. commune as the reference outcome.

RESULTS: Overall, 196 specimens were assessed during the study period. Based on the protocol, 19 specimens (10 %) were diagnosed as "a specimen CONTAINING S. commune." All these specimens contained genetically-proven S. commune (positive predictive value: 100 %). S. commune was not recovered from any specimens that the protocol diagnosed as "NOT containing S. commune" (negative predictive value: 100 %).

CONCLUSIONS: This protocol enables the efficient and cost-effective detection of S. commune in clinical laboratories in a general medical facility, potentially reducing the underdiagnosis of S. commune-related allergic airway diseases and improving medical resource use.