Molecular characterization and antifungal susceptibility profile of Podospora bulbillosa keratitis: case series and review of literature.

PURPOSE: Podospora species are rarely reported as etiological agents of keratitis. This study reports a series of fungal keratitis caused by Podospora bulbillosa, detailing their clinical presentation, treatment outcomes, in vitro antifungal susceptibility and molecular characterization.

METHODS

Cases of fungal keratitis caused by Podospora bulbillosa between January-March 2025, were retrospectively reviewed from the electronic medical records (EMR). Following microbiological work up, fungal identification was confirmed by large subunit 28S and internal transcribed spacer (ITS) region sequencing and molecular phylogenetic tree was constructed by Maximum Likelihood method. In vitro antifungal susceptibility testing was conducted using the Clinical & Laboratory Standards Institute (CLSI) broth microdilution method (M38-A2).

RESULTS

Five male patients (aged 5-72 years) presented with Podospora bulbillosa keratitis, all following ocular trauma as the predisposing factor. Clinical presentation included central or paracentral pigmented plaque-like stromal infiltrates with surrounding edema and varying degrees of thinning and hypopyon in advanced cases. All patients received topical natamycin 5 % as primary therapy; while one case involved polymicrobial infection with Corynebacterium pseudodiphtheriticum. Three patients showed clinical resolution with scarring following medical management alone. All Podospora bulbillosa isolates showed low MICs (0.03-0.125 µg/mL) to natamycin, azoles, echinocandins, and amphotericin B, indicating potent in vitro activity.

CONCLUSION

Notably, all five P. bulbillosa isolates clustered within a single subclade, indicating close genetic relatedness. Podospora bulbillosa keratitis responds well to standard antifungal agents. Molecular tools are crucial for accurate identification of rare, non-sporulating fungal pathogens.