Molecular Identification, Antifungal Susceptibility Profile, and Biofilm Formation of Clinical and Environmental Rhodotorula Species Isolates

Abstract

Rhodotorula species are emergent fungal pathogens capable of causing invasive infections, primarily fungemia. They are particularly problematic in immunosuppressed patients when using a central venous catheter. In this study, we evaluated the species distribution of 51 clinical and 8 environmental Rhodotorula species isolates using the ID32C system and internal transcribed spacer (ITS) sequencing. Antifungal susceptibility testing and biofilm formation capability using a crystal violet staining assay were performed. Using ITS sequencing as the gold standard, the clinical isolates were identified as follows: 44 R. mucilaginosa isolates, 2 R. glutinis isolates, 2 R. minuta isolates, 2 R. dairenensis isolates, and 1 Rhodosporidium fluviale isolate. The environmental isolates included 7 R. mucilaginosa isolates and 1 R. slooffiae isolate. Using the ID32C system, along with a nitrate assimilation test, only 90.3% of the isolates tested were correctly identified. In the biofilm formation assay, R. mucilaginosa and R. minuta exhibited greater biofilm formation ability compared to the other Rhodotorula species; the clinical isolates of R. mucilaginosa showed greater biofilm formation compared to the environmental isolates (P ‫؍‬ 0.04). Amphotericin B showed good in vitro activity (MIC < 1 g/ml) against planktonic cells, whereas voriconazole and posaconazole showed poor activity (MIC 50 / MIC 90 , 2/4 g/ml). Caspofungin and fluconazole MICs were consistently high for all isolates tested (>64 g/ml and > 4 g/ml, respectively). In this study, we emphasized the importance of molecular methods to correctly identify Rhodotorula species isolates and non-R. mucilaginosa species in particular. The antifungal susceptibility profile reinforces amphotericin B as the antifungal drug of choice for the treatment of Rhodotorula infections. To our knowledge, this is the first study evaluating putative differences in the ability of biofilm formation among different Rhodotorula species.

Biofilm Production and Antibiofilm Activity of Echinocandins and Liposomal Amphotericin B in Echinocandin-Resistant Yeast Species

“…Liposomal amphotericin B had the highest activity against biofilms formed by isolates with acquired resistance (the P value was not significant) or intrinsic resistance (P Ͻ 0.05) to echinocandins; this finding is consistent with other studies, where conventional amphotericin B had high anti-biofilm activity, even against non-Candida isolates (25)(26)(27)(28)(29). However, we observed that biofilms formed by C. tropicalis isolates were highly resistant to liposomal amphotericin B, which was unable to achieve an 80% reduction in the metabolic activity of the biofilm.…”

An unusual case of Rhodotorula mucilaginosa fungaemia in a cancer patient

“…They are commonly recovered from human skin, lungs, conjunctivae, urine and gastrointestinal tract (1). Though it is a saprophyte, its isolation from blood cultures and other sterile fluids such as cerebrospinal fluid can be relevant when contamination is ruled out (4). Indeed, Rhodotorula spp.…”

“…However, bloodstream infection due to Rhodotorula is extremely rare and mostly associated with underlying immunosuppression or cancer [4,7,8].…”

Rhodotorula Fungaemia in a Preterm Infant with umbilical Venous Catheter and Parenteral Nutrition Intraperitoneal Extravasation

“…The species shows resistance to echinocandins with high MIC50 >8ug/mL and Fluconazole resistance (MIC50 >128ug/mL) [14]. Although the mechanism of resistance has not been reported, the consistently high MICs suggest intrinsic resistance to echinocandins and triazoles [9].…”

“…The species produces a biofilm which may play a role in the association with CVCs, particularly with R. mucilaginosa and R. Minuta [9]. Environmental contamination of invasive prosthetic devices at the time of insertion may act as point of entry into the host and conditions that compromise immunity may make the organism pathogenic [8].…”