Candida auris susceptibility on surfaces coated with the antifungal drug caspofungin.

Candida auris is known to survive for weeks on solid material surfaces. Its longevity contributes to medical device contamination and spread through healthcare facilities. We fabricated antifungal surface coatings by coating plastic and glass surfaces with a thin polymer layer to which the antifungal drug caspofungin was covalently conjugated. Caspofungin-susceptible and -resistant C. auris strains were inhibited on these surfaces by 98.7 and 81.1%, respectively. Cell viability studies showed that this inhibition was fungicidal. Our findings indicate that C. auris strains can be killed on contact when exposed to caspofungin that is reformulated as a covalently-bound surface layer. LAY SUMMARY: Candida auris is pathogenic, multidrug resistant yeast with the ability to survive on surfaces and remain transmissible for long periods of time in healthcare settings. In this study, we have prepared an antifungal surface coating and demonstrated its ability to kill adhering C. auris cells on contact.

Structure, Mechanism, and Inhibition of Aspergillus fumigatus Thioredoxin Reductase.

Aspergillus fumigatus infections are associated with high mortality rates and high treatment costs. Limited available antifungals and increasing antifungal resistance highlight an urgent need for new antifungals. Thioredoxin reductase (TrxR) is essential for maintaining redox homeostasis and presents as a promising target for novel antifungals. We show that ebselen [2-phenyl-1,2-benzoselenazol-3(2H)-one] is an inhibitor of A. fumigatus TrxR (Ki = 0.22 µM) and inhibits growth of Aspergillus spp., with in vitro MIC values of 16 to 64 µg/ml. Mass spectrometry analysis demonstrates that ebselen interacts covalently with a catalytic cysteine of TrxR, Cys148. We also present the X-ray crystal structure of A. fumigatus TrxR and use in silico modeling of the enzyme-inhibitor complex to outline key molecular interactions. This provides a scaffold for future design of potent and selective antifungal drugs that target TrxR, improving the potency of ebselen toward inhbition of A. fumigatus growth.

Visualizing Biomaterial Degradation by Candida albicans Using Embedded Luminescent Molecules To Report on Substrate Digestion and Cellular Uptake of Hydrolysate.

Microbial pathogens use hydrolases as a virulence strategy to spread disease through tissues and colonize medical device surfaces; however, visualizing this process is a technically challenging problem. To better understand the role of secreted fungal hydrolases and their role in Candida albicans virulence, we developed an in situ model system using luminescent Re(I) and Ir(III) containing probe molecules embedded in a biodegradable (poly(lactic-co-glycolic acid), PLGA) polymer and tracked their uptake using epifluorescent imaging. We found that secretion of esterases can explain how physically embedded probes are acquired by fungal cells through the degradation of PLGA since embedded probes could not be liberated from nonbiodegradable polystyrene (PS). It was important to verify that epifluorescent imaging captured the fate of probe molecules rather than naturally occurring fungal autofluorescence. For this, we exploited the intense luminescent signals and long spectral relaxation times of the Re and Ir containing probe molecules, resolved in time using a gated imaging system. Results provide a visual demonstration of a key virulence trait of C. albicans: the use of hydrolases as a means to degrade materials and acquire hydrolysis products during fungal growth and hyphal development. These results help to explain the role of nonspecific hydrolases using a degradable material that is relevant to the study of fungal pathogenesis on biotic (tissues) surfaces. Additionally, understanding how fungal pathogens condition surfaces by using nonspecific hydrolases is important to the study of fungal attachment on abiotic surfaces, the first step in biofilm formation on medical devices.

The importance of fungal pathogens and antifungal coatings in medical device infections.

In recent years, increasing evidence has been collated on the contributions of fungal species, particularly Candida, to medical device infections. Fungal species can form biofilms by themselves or by participating in polymicrobial biofilms with bacteria. Thus, there is a clear need for effective preventative measures, such as thin coatings that can be applied onto medical devices to stop the attachment, proliferation, and formation of device-associated biofilms. However, fungi being eukaryotes, the challenge is greater than for bacterial infections because antifungal agents are often toxic towards eukaryotic host cells. Whilst there is extensive literature on antibacterial coatings, a far lesser body of literature exists on surfaces or coatings that prevent attachment and biofilm formation on medical devices by fungal pathogens. Here we review strategies for the design and fabrication of medical devices with antifungal surfaces. We also survey the microbiology literature on fundamental mechanisms by which fungi attach and spread on natural and synthetic surfaces. Research in this field requires close collaboration between biomaterials scientists, microbiologists and clinicians; we consider progress in the molecular understanding of fungal recognition of, and attachment to, suitable surfaces, and of ensuing metabolic changes, to be essential for designing rational approaches towards effective antifungal coatings, rather than empirical trial of coatings.

Surface coatings with covalently attached caspofungin are effective in eliminating fungal pathogens.

In this work we have prepared surface coatings formulated with the antifungal drug caspofungin, an approved pharmaceutical lipopeptide compound of the echinocandin drug class. Our hypothesis was to test whether an antifungal drug with a known cell-wall disrupting effect could be irreversibly tethered to surface coatings and kill (on contact) biofilm-forming fungal human pathogens from Candida spp. The first aim of the study was to use surface analysis to prove that the chemical binding to the surface polymer interlayer was through specific and irreversible bonds (covalent) and not due to non-specific adsorption through weak forces that could be later reversed (physisorption). Secondly, we quantified the antifungal nature of these coatings in a biological assay showing excellent killing against C. albicans and C. tropicalis and moderate killing against C. glabrata and C. parapsilosis. We concluded that caspofungin retains antifungal activity even when it is irreversibly immobilized on a surface, providing a new insight into its mechanism of action. Thus, surface coatings that have echinocandins permanently bound will be useful in preventing the establishment of fungal biofilms on materials.