Reconstructed interfollicular feline epidermis as a model for the screening of antifungal drugs against Microsporum canis

Human skin models: From healthy to disease-mimetic systems; characteristics and applications

Skin drug delivery is an emerging route in drug development, leading to an urgent need to understand the behaviour of active pharmaceutical ingredients within the skin. Given, As one of the body's first natural defences, the barrier properties of skin provide an obstacle to the successful outcome of any skin drug therapy. To elucidate the mechanisms underlying this barrier, reductionist strategies have designed several models with different levels of complexity, using non-biological and biological components. Besides the detail of information and resemblance to human skin in vivo, offered by each in vitro model, the technical and economic efforts involved must also be considered when selecting the most suitable model. This review provides an outline of the commonly used skin models, including healthy and diseased conditions, in-house developed and commercialized models, their advantages and limitations, and an overview of the new trends in skin-engineered models.

In vitro and ex vivo biofilms of dermatophytes: a new panorama for the study of antifungal drugs

This study describes an ex vivo model that creates an environment for dermatophyte biofilm growth, with features that resemble those of in vivo conditions, designing a new panorama for the study of antifungal susceptibility. Regarding planktonic susceptibility, MIC ranges were 0.125-1 µg ml^-1 for griseofulvin and 0.000097-0.25 µg ml^-1 for itraconazole and terbinafine. sMIC50 ranges were 2->512 µg ml^-1 for griseofulvin and 0.25->64 µg ml^-1 for itraconazole and terbinafine. CLSM images demonstrated a reduction in the amount of cells within the biofilm, but hyphae and conidia were still observed and biofilm biomass was maintained. SEM analysis demonstrated a retraction in the biofilm matrix, but fungal structures and water channels were preserved. These results show that ex vivo biofilms are more tolerant to antifungal drugs than in vitro biofilms, suggesting that environmental and nutritional conditions created by this ex vivo model favor biofilm growth and robustness, and hence drug tolerance.

In vitro models of dermatophyte infection to investigate epidermal barrier alterations

Fungal infections of the skin, known as dermatophytoses, are initiated at the epidermal barrier and lead to dysfunctions of the stratum corneum and cornified skin appendages. Dermatophytosis affects a significant part of the human population and, despite the availability of effective treatments, its prevalence is still increasing. Numerous dermatophyte species are able to induce lesions in both animals and humans, with different clinical pictures and host inflammatory responses. The understanding of the infectious process and of tissue responses has been impeded by discrepancies between observations in vivo or in research models. Indeed, cells cultured as monolayers do not undergo the keratinization process required to study the adherence and invasion of dermatophytes. Animal models lack relevance to study human dermatophytosis because of species-specific differences in the development of lesions and inflammatory responses. This review focuses on the recent development of cultured human skin equivalents, which partly overcomes those limitations and allows improved understanding of the pathogenesis of dermatophytosis in human being, especially the impacts of infection on epidermal barrier integrity.

Ex vivo biofilm-forming ability of dermatophytes using dog and cat hair: an ethically viable approach for an infection model

The aim of this study was to establish an ex vivo model for dermatophyte biofilm growth, using hair from dogs and cats. Strains of Microsporum canis, M. gypseum, Trichophyton mentagrophytes and T. tonsurans were assessed for in vitro and ex vivo biofilm production. All T. mentagrophytes and T. tonsurans isolates and 8/12 M. canis and 1/7 M. gypseum isolates formed biofilms in vitro, while all tested isolates presented biofilm growth on ex vivo models. T. mentagrophytes and M. canis formed more homogeneous and better-structured biofilms with greater biomass production on cat hair but T. tonsurans formed more biofilm on dog hair. Confocal and scanning electron microscopy demonstrated fungal hyphae colonizing and perforating the hair shaft, abundant fungal conidia, biofilm extracellular matrix and biofilm water channels. The present study demonstrated an ex vivo model for the performance of studies on biofilm formation by dermatophytes, using dog and cat hair.

Modeling dermatophytosis in reconstructed human epidermis: A new tool to study infection mechanisms and to test antifungal agents

Dermatophytosis is a superficial fungal infection of keratinized structures that exhibits an increasing prevalence in humans and is thus requesting novel prophylactic strategies and therapies. However, precise mechanisms used by dermatophytes to adhere at the surface of the human epidermis and invade its stratum corneum are still incompletely identified, as well as the responses provided by the underlying living keratinocytes during the infection. We hereby report development of an in vitro model of human dermatophytosis through infection of reconstructed human epidermis (RHE) by arthroconidia of the anthropophilic Trichophyton rubrum species or of the zoophilic Microsporum canis and Arthroderma benhamiae species. By modulating density of arthroconidia in the inoculum and duration of exposure to such pathogens, fungal infection limited to the stratum corneum was obtained, mimicking severe but typical in vivo situation. Fungal elements in infected RHE were monitored over time by histochemical analysis using periodic-acid Schiff-staining or quantified by qPCR-detection of fungal genes inside RHE lysates. This model brings improvements to available ones, dedicated to better understand how dermatophytes and epidermis interact, as well as to evaluate preventive and therapeutic agents. Indeed, miconazole topically added to RHE was demonstrated to inhibit fungal infection in this model.

Feline dermatophytosis: aspects pertinent to disease management in single and multiple cat situations

PRACTICAL RELEVANCE

Dermatophytosis (ringworm) is a superficial fungal skin disease of cats that, depending on the geographic region and practice caseload, may be encountered uncommonly through to commonly. This is a self-curing disease in an immunocompetent cat.

GLOBAL IMPORTANCE

Dermatophytosis is prevalent worldwide and is one of a number of zoonotic skin diseases that cat owners are at risk of contracting.

CLINICAL CHALLENGES

Dermatophytosis causes non-specific signs of hair loss, erythema and scaling, making it a differential diagnosis for many skin diseases of cats. The fact that this disease is infectious and contagious, and does not have any one classic clinical presentation, makes knowledge of diagnostic tools important in detection. The veterinarian's role is in early disease recognition and institution of appropriate therapy to hasten resolution of the disease.

AIM

The focus of this article is to provide an update and review of the most pertinent aspects that may be helpful in the management of dermatophytosis in any single or multiple cat situation.

EVIDENCE BASE

Where appropriate, evidence from the literature is used to supplement a summary of the author's clinical experience and research in feline dermatophytosis.

Mechanisms of skin adherence and invasion by dermatophytes

Dermatophytes are keratinophilic fungi that can be pathogenic for humans and animals by infecting the stratum corneum, nails, claws or hair. The first infection step consists of adherence of arthroconidia to the stratum corneum. The mechanisms and the kinetics of adherence have been investigated using different in vitro and ex vivo experimental models, most notably showing the role of a secreted serine protease from Microsporum canis in fungal adherence to feline corneocytes. After germination of the arthroconidia, dermatophytes invade keratinised structures that have to be digested into short peptides and amino acids to be assimilated. Although many proteases, including keratinolytic ones, have been characterised, the understanding of dermatophyte invasion mechanisms remains speculative. To date, research on mechanisms of dermatophyte infection focused mainly on both secreted endoproteases and exoproteases, but their precise role in both fungal adherence and skin invasion should be further explored.

Development of three-dimensional tissue-engineered models of bacterial infected human skin wounds

While infected skin wounds are on the increase because of ageing populations, rising incidence of diabetes, and antibiotic resistance, we lack relevant in vivo or in vitro models to study many aspects of bacterial interaction with skin. The aim of this study was to develop three-dimensional models of normal human skin to study bacterial infection. The common dermatological pathogens Staphylococcus aureus and Pseudomonas aeruginosa were used to infect tissue-engineered skin, and the course of infection in the skin was examined over several days. Two forms of model were developed-one in which bacteria were introduced directly to 10 mm wounds in the epidermis, and another in which wounds were created by burning a 4 mm hole in the center of the tissue before inoculation. The bacteria flourished within the engineered skin, and colonized the upper epidermal layers before invasion into the dermis. Infection with P. aeruginosa caused a loss of epidermis and de-keratinization of the skin constructs, as well as partial loss of basement membrane. These novel complex human skin infection models could be used to investigate microbial invasion of normal skin epithelium, basement membrane, and connective tissue, and as a model to study approaches to reduce bacterial burden in skin wounds.