Emerging ocular pathogen: multidrug-resistant Corynespora cassiicola in fungal keratitis: case series and literature review

Abstract

Purpose: To describe the clinical presentation, microbiological and molecular identification, antifungal susceptibility profile, and outcomes of four patients with fungal keratitis caused by Corynespora cassiicola, an emerging and rarely reported ocular pathogen.

Methods: This retrospective case series includes four culture-confirmed cases of C. cassiicola keratitis diagnosed at a tertiary eye care centre in South India. Microbiological evaluation included direct microscopy, culture, and morphological identification. Molecular confirmation was performed using internal transcribed spacer (ITS) region sequencing. Phylogenetic analysis was conducted to assess genetic relatedness. Antifungal susceptibility testing was performed using broth microdilution methods as per CLSI guidelines.

Results: All patients presented unilateral corneal ulcers, following ocular trauma. Microscopy revealed septate hyphae; cultures yielded slow-growing, darkly pigmented fungi identified as Corynespora cassiicola. ITS sequencing confirmed the identity, with all isolates clustering within a well-supported C. cassiicola clade in the phylogenetic tree. MIC testing showed variable susceptibility to natamycin and amphotericin B, with lower MICs for azoles such as voriconazole and posaconazole. Three patients showed poor response to medical therapy and were planned for therapeutic penetrating keratoplasty, and one was lost to follow-up.

Conclusion: Corynespora cassiicola is an uncommon cause of fungal keratitis, often associated with agricultural trauma. Accurate identification through molecular methods is essential for appropriate management. This case series represents the first comprehensive report of multiple keratitis cases caused by C. cassiicola, highlighting its clinical significance and microbiological profile.

Keywords: Corynespora spp.; Antifungal susceptibility; Dematiaceous mold; ITS PCR; Keratitis.