Ocular infections by melanized fungi Curvularia lunata and Lasiodiplodia theobromae: antifungal susceptibility, clinical outcome, and clinico-microbiological correlation.

Abstract

Abstract Purpose: Antifungal resistance is on the rise, with limited number of antifungals available for clinical use and very few new ones in the pipeline. Melanized fungal pathogens have been rarely studied for their antifungal susceptibility patterns and clinical outcomes, though they are the second most common cause of fungal ocular infections after hyaline fungi. Our study aims to report the antifungal susceptibility, clinical outcomes, and clinico-microbiological correlation of two common melanized fungi Curvularia lunata and Lasiodiplodia theobromae isolated from ocular infections. Method: Antifungal susceptibility testing (AFST) was performed by broth microdilution technique as per standard guidelines in 30 isolates (17 C. lunata and 13 L. theobromae). Antifungal panel tested consisted of the polyenes amphotericin B and natamycin, the azoles voriconazole, ketoconazole, posaconazole, itraconazole and fluconazole, and the echinocandin caspofungin. Isolates resistant to more than or equal to two classes of antifungals were considered as multidrug resistant (MDR). DNA sequencing was performed for subset of isolates for species confirmation following conventional mycology. Statistical analysis consisted of both descriptive statistics and multivariate analysis. Results: Isolates showed highest susceptibility to voriconazole (83.3% isolates), followed by natamycin (80%), fluconazole (80%), itraconazole (76.7%), ketoconazole (70%), posaconazole (66.7%), caspofungin (66.7%) and amphotericin B (63.3%), though MIC50 was on the lower side for all the antifungals. All patients were empirically administered topical natamycin with additional oral ketoconazole or intraocular voriconazole in select patients. Multivariate analysis suggested strong association between MDR and poor clinical outcome (p=0.03, odds ratio=7.8). All patients presented with microbial keratitis and one progressed to endophthalmitis. Surgical management with therapeutic penetrating keratoplasty (TPK) were required in 40% of patients. Good anatomical outcome was observed in 80% of patients, half of whom had good visual outcome too. Poor anatomical and visual outcome were observed in 20% of patients. DNA sequencing of subset of study isolates showed Curvularia lunata to be the highest Curvularia spp. study isolates (n=5/7). Histopathological examination of excised corneal buttons (TPK) showed fungal filaments in 66.7% (n=8/12) of cases. Conclusion: Melanized fungi causing ocular infections have varying in-vitro susceptibility to different antifungal agents and clinical outcome. Voriconazole showed significantly higher and amphotericin B lower activity in-vitro for the fungi. The MDR isolates showed poorer clinical outcomes.