Development of a new medium useful for the recovery of dermatophytes from clinical specimens by minimizing the carryover effect of antifungal agents

Reappraisal of Conventional Diagnosis for Dermatophytes

Dermatophytoses include a wide variety of diseases involving glabrous skin, nails and hair. These superficial infections are a common cause of consultation in dermatology. In many cases, their diagnosis is not clinically obvious, and mycological analysis therefore is required. Direct microscopic examination of the samples using clearing agents provides a quick response to the clinician and is usually combined with cultures on specific media, which must be used to overcome the growth of contaminating moulds that may hamper the recovery of dermatophytes. Accurate identification of the causative agent (i.e. at the species level), currently based on morphological criteria, is necessary not only to initiate an appropriate treatment but also for setting prophylactic measures. However, conventional methods often lack sensitivity and species identification may require up to 4 weeks if subcultures are needed. Histological analysis, which is considered the "gold standard" for the diagnosis of onychomycoses, is seldom performed, and as direct examination, it does not allow precise identification of the pathogen. Nevertheless, a particular attention to the quality of clinical specimens is warranted. Moreover, the sensitivity of direct examination may be greatly enhanced by the use of fluorochromes such as calcofluor white. Likewise, sensitivity of the cultures could be enhanced by the use of culture media containing antifungal deactivators. With the generalization of molecular identification by gene sequencing or MALDI-TOF mass spectrometry, the contribution of historical biochemical or physiological tests to species identification of atypical isolates is now limited. Nevertheless, despite the recent availability of several PCR-based kits and an extensive literature on molecular methods allowing the detection of fungal DNA or both detection and direct identification of the main dermatophyte species, the biological diagnosis of dermatophytosis in 2016 still relies on both direct examination and cultures of appropriate clinical specimens.

Tinea pedis: the etiology and global epidemiology of a common fungal infection

Tinea pedis, which is a dermatophytic infection of the feet, can involve the interdigital web spaces or the sides of the feet and may be a chronic or recurring condition. The most common etiological agents are anthropophiles, including Trichophyton rubrum sensu stricto, which is the most common, followed by Trichophyton interdigitale and Epidermophyton floccosum. There has been a change in this research arena, necessitating a re-evaluation of our knowledge on the topic from a multidisciplinary perspective. Thus, this review aimed to provide a solid overview of the current status and changing patterns of tinea pedis. The second half of the twentieth century witnessed a global increase in tinea pedis and a clonal spread of one major etiologic agent, T. rubrum. This phenomenon is likely due to increases in urbanization and the use of sports and fitness facilities, the growing prevalence of obesity and the aging population. For optimal patient care and management, the diagnosis of tinea pedis should be verified by microbiological analysis. In this review, we discuss the epidemiology, clinical forms, complications and mycological characteristics of tinea pedis and we highlight the pathogenesis, prevention and control parameters of this infection.

Short-term therapy with luliconazole, a novel topical antifungal imidazole, in guinea pig models of tinea corporis and tinea pedis

Luliconazole is a novel topical antifungal imidazole with broad-spectrum and potent antifungal activity. The drug is under clinical development in the United States for management of dermatophytosis with a short-term treatment regimen. The present study was undertaken to investigate the clinical benefit of short-term therapy with luliconazole cream in guinea pig models of tinea corporis and tinea pedis induced with Trichophyton mentagrophytes. The dose-dependent therapeutic efficacy of topical luliconazole cream (0.02 to 1%), measured by macroscopic improvement of skin lesions and by fungal eradication as determined by a culture assay, was demonstrated using a tinea corporis model. The improvement in skin lesions seen with luliconazole cream was observed even at a concentration of 0.02%, and its efficacy at 0.1% was equal to that of 1% bifonazole cream. The efficacy of short-term therapy with 1% luliconazole cream, which is used for clinical management, was investigated using the tinea corporis model (4- and 8-day treatment regimens) and the tinea pedis model (7- and 14-day treatment regimens). The 1% luliconazole cream completely eradicated the fungus in half or less of the treatment time required for 1% terbinafine cream and 1% bifonazole cream, as determined by a culture assay for both models. These results clearly indicate that 1% luliconazole cream is sufficiently potent for short-term treatment for dermatophytosis compared to existing drugs. Luliconazole is expected to be useful in the clinical management of dermatophytosis.

Animal model of dermatophytosis

Dermatophytosis is superficial fungal infection caused by dermatophytes that invade the keratinized tissue of humans and animals. Lesions from dermatophytosis exhibit an inflammatory reaction induced to eliminate the invading fungi by using the host's normal immune function. Many scientists have attempted to establish an experimental animal model to elucidate the pathogenesis of human dermatophytosis and evaluate drug efficacy. However, current animal models have several issues. In the present paper, we surveyed reports about the methodology of the dermatophytosis animal model for tinea corporis, tinea pedis, and tinea unguium and discussed future prospects.

Conventional methods for the diagnosis of dermatophytosis

Dermatophytes are keratinolytic fungi responsible for a large variety of diseases that can affect glabrous skin, nails and hair. In many cases, the diagnosis is not clinically obvious, and mycological analysis is required. This includes both direct microscopic examination and cultures. First of all, clinical specimens have to be sampled according to localization and characteristics of the lesions. Direct microscopic examination is usually performed using clearing reagents (KOH or Amman's chloral-lactophenol), but its sensitivity may be greatly enhanced by the use of stains or fluorochromes such as Congo red or Calcofluor white. Histological analysis is an efficient method, but it is constraining for the patients and, as direct examination, it does not allow precise identification of the pathogen. Cultures are therefore needed, and specific culture media may be used to overcome the growth of rapidly growing contaminating moulds which may hamper the recovery of dermatophytes. Identification at the species level which may be useful to initiate an appropriate treatment or for setting prophylactic measures, relies on macroscopic and microscopic morphology. Subcultures on culture media which stimulate conidiation and, for some species, the production of pigments, are often necessary. Additionally, in case of atypical isolates, some biochemical or physiological tests may be performed such as the search for urease activity or the in vitro hair perforation test. However, their contribution to species identification is rather limited, and progress is still needed for the development of biochemical or immunological tests allowing an accurate identification at the species level, pending for the availability of molecular biology-based kits.

Evaluation of combined deactivators-supplemented agar medium (CDSAM) for recovery of dermatophytes from patients with tinea pedis

Using a newly-developed medium, i.e., combined deactivators-supplemented agar medium (CDSAM), the viability of dermatophytes in skin scales was evaluated. Culture studies were conducted with skin scales collected from 44 patients with tinea pedis who had been treated for two weeks with topical antifungal drugs. Sixty-four percent of the specimens were mycologically positive on CDSAM, while only 23% of these same specimens were positive when cultured on conventional Sabouraud's dextrose agar medium (SDA). Alternatively, 36% of all cases were negative on both media. The experimental data from this clinical study indicate that CDSAM was more useful than SDA in accurately evaluating the efficacy of antifungal drugs since the former minimized the residual effects of drug residues remaining in the skin samples.

Feasibility of using collagen as the base of the antifungal drug, miconazole

The feasibility of using collagen as the base of miconazole was investigated. The addition of 33% collagen to a miconazole solution did not affect the minimal inhibitory concentration (MIC80) of the miconazole solution for Candida albicans. When 1 microg mL(-1) of miconazole in 33% collagen solution was plated on resin discs and dried to yield a thin membrane, the growth of C. albicans on the resin discs was nearly completely inhibited. In addition, we compared the antifungal effect of this collagen solution that contained 1 microg mL(-1) miconazole, with the antifungal effect of miconazole gel that had been diluted with glycerol (the main component of miconazole gel) to yield a final concentration of 1 microg mL(-1) of miconazole; as a result, we found that the collagen solution containing 1 microg mL(-1) miconazole had a stronger antifungal effect. In conclusion, our results demonstrated that it may be feasible to use collagen as the base of miconazole instead of glycerol, and suggest that a collagen-based miconazole solution would have a stronger antifungal effect than commercially available miconazole gel. Collagen-based miconazole solution may be useful for the treatment of Candida-associated denture stomatitis.

A novel mycological analysis valuable for evaluating therapeutic efficacy of antimycotics against experimental dermatophytosis in guinea pigs

Although antimycotic effects are mainly evaluated with regard to whether or not the fungi grow from a specimen obtained from the drug-treated skin, the potential for discrepancies in skin specimens in which the fungi are grown has not been evaluated, in the experimental tinea model. In this study, to evaluate the therapeutic effectiveness of antimycotic agents against fungal skin infection, a novel form of mycological assessment, which focuses on the size of colonies grown from skin specimens was examined and developed. When microconidia of Trichophyton mentagrophytes were inoculated onto a Sabouraud dextrose agar (SDA) plate and incubated at 27 degrees C for 5 days, a linear relationship was observed between the growth area of mycelia and the logarithm of the quantity of microconidia. This relationship between the growth area and the logarithm of the number of T. mentagrophytes microconidia did not change with the addition of skin homogenate and/or keratin powder. Next, the number of fungi in skin blocks attendant upon experimental, cutaneous infection in guinea pigs was evaluated and analyzed via a calibration curve, determined based on a microconidium suspension of T. mentagrophytes. Estimates of severity of dermatophytic infection in experimental animals were parallel to, but more reliable than, results obtained via the conventional mycological method (fungus-positive skin ratio of treated skin) in culture studies of infected dermal tissues. This new analytical method may also be applicable to the in vivo assessment of the therapeutic effect against dermatophytosis experimentally produced in guinea pigs.

A novel method using micropig stratum corneum in vitro for the evaluation of anti-Trichophyton mentagrophytes activity

Antifungal susceptibility testing under conditions close to clinical status is expected to provide more helpful information than that obtained by a conventional microdilution method. For this purpose, we developed a novel method to evaluate anti-Trichophyton mentagrophytes activity of antifungal agents in vitro by using disks of micropig stratum corneum epidermis (SCE). Basal agar medium containing K2HPO4, MgSO4, CaCl2 and three kinds of antibiotics. Bifonazole (BFZ), lanoconazole (LCZ) or terbinafine (TBF) was added to the basal agar medium to give serially doubling dilutions ranging from 0.0006 to 10 microg/ml. Five-hundred-microl portions of the agar media thus prepared were solidified in wells of flat-bottomed plates. SCE disks (6 mm in diameter) were placed on surfaces of the agar medium and 10(4) conidia of T. mentagrophytes were inoculated on each SCE disk. There was very good correlation between the initial concentration of the antifungal agents added to the basal agar medium (microg/ml) and the concentration of the agents impregnated into the SCE disks (microg/g) (r2>0.99). The minimum inhibitory concentration (MIC) values of BFZ, LCZ and TBF were respectively 26-, 10- and 78-times higher than those measured by the standard microdilution method. From the correlation between the concentration of the agents in the basal medium and that in the SCE disks, the above MIC values corresponded to the concentrations in SCE disks (microg/g), 832.95 for BFZ, 1.42 for LCZ and 8.87 for TBF. This novel method of antidermatophytic susceptibility testing using SCE would be useful as an in vitro screening of proper antimycotics for topical treatment of dermatophytosis.