A New Medium That Promotes Mass Sporulation of Trichophyton rubrum In Vitro

Trichophyton rubrum is one of the most common human pathogenic fungi, with the infections often managed through empirical drug use. However, treatments frequently lead to relapse upon withdrawal. The rise in drug-resistant T. rubrum cases has led to an increased demand for drug susceptibility assays in clinical settings to guide antifungal drug selection and monitor therapeutic outcomes. However, insufficient sporulation of T. rubrum on routinely-used media presents a significant challenge, limiting the widespread use of drug sensitivity tests on a large scale. There is an urgent need to develop a new, effective culture method that can promote rapid and abundant sporulation of T. rubrum. In this study, we adopted a nutrient-rich medium (Yeast extract-glucose YAG) which demonstrated superior efficacy in promoting T. rubrum sporulation compared to PDA and OA mediums. Abundant microconidia production of T. rubrum was observed at 30° between 7 to 10 days on YAG medium, and this sporulation was further enhanced under elevated carbon dioxide conditions. Particularly, a 20% carbon dioxide environment significantly improved T. rubrum sporulation on PDA by 30-fold, equivalent to the sporulation effect with YAG cultivation. This enhanced sporulation was confirmed in 37 clinical T. rubrum isolates, highlighting the potential applicability of YAG medium in both clinical and research settings for drug susceptibility assays and pathogenesis studies. These findings also offer new insights into improving sporulation in other fungi with low spore production.