Species identification, antifungal susceptibility profiles and biofilm formation attributes of Rhodotorula isolates from ocular infections

Background: Members of genus Rhodotorula are widely distributed in nature and have been traditionally considered non-pathogenic. Last few decades have seen the yeast as an emerging pathogen. We observed increase in numbers of Rhodotorula isolates from ocular infections in last few years, thus this prospective study was planned. Objectives: To identify the species of Rhodotorula isolates from ocular infections. To know the antifungal susceptibilities and study the biofilm formation attributes of the isolates. Materials and Methods: Rhodotorula isolates were speciated using conventional methods, Matrix Assisted Laser Desorption and Ionisation – Time of Flight (MALDI- TOF) and sequencing of ITS region of ribosomal DNA. Antifungal susceptibility testing (AFST) was done using disc diffusion and E-test. Biofilm formation was studied using XTT [2,3-bis (2-methoxy-4-nitro-5-sulfo-phenyl)-2H-tetra-zolium-5-carboxanilide] assay. Results: Twenty four isolates (92.3%) were identified as R. mucilaginosa and two as R. Minuta. AFST showed high MICs against Fluconazole, Amphotericin-B, Caspofungin, Micafungin and Flucytosine; MIC distribution from low to very high against Voriconazole, Itraconazole and Natamycin; and very low MICs against Posaconazole 57.7% of isolates were strong biofilm producers, 23.1% were moderate, and 19.2% were non producers. Conclusions: This is the first prospective study on species distribution, antifungal susceptibility and biofilm production attributes of Rhodotorula isolates from ocular infections; also first time demonstrating the utility of proteomics based MALDI-TOF in diagnosing Rhodotorula up to species level. The study has shown high MICs against the conventional azoles, Amphotericin-B and Flucytosine. However, low MICs against Posaconazole and Natamycin give a hope for their possible therapeutic use.