Malassezia colonisation on a reconstructed human epidermis: Imaging studies

Abstract

Summary Background Biofilm formation represents a major microbial virulence attribute especially at epithelial surfaces such as the skin. Malassezia biofilm formation at the skin surface has not yet been addressed. Objective The present study aimed to evaluate Malassezia colonisation pattern on a reconstructed human epidermis (RhE) by imaging techniques. Methods Malassezia clinical isolates were previously isolated from volunteers with pityriasis versicolor and seborrhoeic dermatitis. Yeast of two strains of M furfur and M sympodialis were inoculated onto the SkinEthic™ RHE. The tissues were processed for light microscopy, wide‐field fluorescence microscopy and scanning electron microscopy. Results Colonisation of the RhE surface with aggregates of Malassezia yeast entrapped in a multilayer sheet with variable amount of extracellular matrix was unveiled by imaging techniques following 24, 48, 72 and 96 hours of incubation. Whenever yeast were suspended in RPMI medium supplemented with lipids, the biofilm substantially increased with a dense extracellular matrix in which the yeast cells were embedded. Slight differences were found in the biofilm architectural structure between the two tested species with an apparently higher entrapment and viscosity in M furfur biofilm. Conclusion Skin isolates of M furfur and M sympodialis were capable of forming biofilm in vitro at the epidermal surface simulating in vivo conditions. Following 24 hours of incubation, without added lipids, rudimental matrix was barely visible, conversely to the reported at plastic surfaces. The amount of biofilm apparently increased progressively from 48 to 96 hours. A structural heterogeneity of biofilm between species was found.

Malassezia spp. Yeasts of Emerging Concern in Fungemia

“…In particular, the ability to produce enzymes such as lipases and/or phospholipases, production of various indolic compounds, the ability to form biofilms, and allergen enriched nanovesicle production were described for M. furfur and M. sympodialis which are frequently related to fungemia. The properties of these microorganisms to adhere to the skin and to medical indwelling devices by forming biofilms influence the antifungal profile of cells, which might represent another virulence factor in fungemia of severely immunocompromised hosts (Figueredo et al, 2013 ; Pedrosa et al, 2019a ). Interestingly the structure of Malassezia biofilms is strain dependent and those of M. furfur and M. pachydermatis from skin lesions are composed of a more gelatinous extracellular matrix (Figueredo et al, 2013 ; Angiolella et al, 2018 ; Pedrosa et al, 2019a ).…”

“…The properties of these microorganisms to adhere to the skin and to medical indwelling devices by forming biofilms influence the antifungal profile of cells, which might represent another virulence factor in fungemia of severely immunocompromised hosts (Figueredo et al, 2013 ; Pedrosa et al, 2019a ). Interestingly the structure of Malassezia biofilms is strain dependent and those of M. furfur and M. pachydermatis from skin lesions are composed of a more gelatinous extracellular matrix (Figueredo et al, 2013 ; Angiolella et al, 2018 ; Pedrosa et al, 2019a ). Since the extracellular matrix is directly linked to the virulence of these yeasts, M. furfur and M.pachydermatis should be more virulent than M. sympodialis , which may explain the lower observed incidence of M. sympodialis fungemia (Figueredo et al, 2013 ; Angiolella et al, 2018 ; Pedrosa et al, 2019a ).…”

“…Biofilm formation has been linked to increased drug resistance and virulence. M. furfur, M. sympodialis , and M. pachydermatis are able to form biofilms, a process that seems to be strain dependent (Figueredo et al, 2013 ; Angiolella et al, 2017 ; Pedrosa et al, 2019a ). In particular, M. pachydermatis strains isolated from dogs with and without skin lesions were able to form biofilms with variable extracellular matrix (ECM) quantity and structure depending on the sources (Figueredo et al, 2013 ).…”

“…In particular, M. pachydermatis strains isolated from dogs with and without skin lesions were able to form biofilms with variable extracellular matrix (ECM) quantity and structure depending on the sources (Figueredo et al, 2013 ). Accordingly, a structural heterogeneity of biofilm was found between those formed by M. furfur and M. sympodialis isolates, with both species exhibiting yeast aggregates in multilayer clusters but with a denser entrapment by a more gelatinous ECM in case of M. furfur biofilms (Pedrosa et al, 2019a ). Biofilm formation and the extracellular matrix generation were responsible for the emergence of antifungal resistance (Figueredo et al, 2013 ; Angiolella et al, 2017 ).…”

Epidermal Regeneration Induced by Comfrey Extract: A Study by Light and Electron Microscopy

“…This study addresses the effects of comfrey herb cream on skin regeneration in a 3-dimensional human skin model of reconstructed human epidermis (RhE). RhE models are commercially available and typically used in skin studies [21] including studies using imaging techniques [22], especially in studies related to skin irritation as a replacement of animal experiments [23]. The RhE model is even recommended for the official OECD test method No.…”