Identifier: TDX:497
Authors: Fernández Torres, Belkys
Abstract:
Dermatophytes are molds that produce infections in the skin, hair and nails of humans and animals. They are usually restricted to the superficial layers of the skin and appendices but they can also affect the dermis and the subcutaneous tissue, thus causing granulomas or pseudomycetomas.Some health science professionals regard dermatophytes as a merely cosmetic problem. The real impact of these infections on the quality of life of the patients involved, however, is considerable. Patients suffering from dermatophyte infections are affected physically since they feel pain, pruritus and discomfort. They may also be affected socially, being regarded by others as lacking basic personal hygiene or as potential sources of infection. And patients who work in the food industry or in other professions where they come into contact with the public may see their careers conditioned or even truncated. These problems are exacerbated in patients suffering from chronic dermatophytoses such as onychomycosis or tinea pedis. In the case of onychomycosis, treatment failure can be as high as 25%. In the case of tinea pedis, especially moccasin-type tinea pedis, the infection may last for years and the frequency of recurrence is as high as 70%.As the treatment of dermatophytoses tends to be prolonged (since the infection is usually chronic), and as the available treatments are not very effective anyway, antifungal drug consumption and public health expenditure are high. In Spain, for example, the annual consumption of topical antifungals involves a cost of approximately 36 million euros and the consumption of systemic antifungals approximately 27,000 euros.To alleviate this problem, new antifungals are being developed. This has generated interest in testing the susceptibility of dermatophytes to these antifungals in a reproducible way. However, no reference methods for this type of fungus currently exist.In this doctoral thesis we have developed and standardized several useful methods for determining the susceptibility of dermatophytes to various antifungals. The methods tested were broth microdilution, Sensititre Yeast One®, agar dilution, Etest®, and disk diffusion. These methods were evaluated with a high number of strains from almost every species of dermatophyte and a large number of antifungals, some of which are already commercially available and some have only recently been synthesised.Our results provide the first database of intra- and interlaboratory reproducibility studies using the microdilution method to determine the optimal test conditions for testing the susceptibility of dermatophytes to the most commonly prescribed antifungals (itraconazole, terbinafine and clotrimazole). These optimal test conditions are: · a final inoculation of 104 ufc/ml, · an incubation time of 7 days,· an incubation temperature of 28º C, and· an endpoint criterion of 100% growth inhibition.We have demonstrated for the first time that two of the commercially available methods for testing the antifungal susceptibility of yeasts (Etest® and Sensititre Yeast One®) can be adapted to test the antifungal susceptibility of dermatophytes. We have also demonstrated that these methods are simple, quick and reproducible in a clinical laboratory. We have shown that the type of inoculum (macroconidia or hyphae), the culture medium, the incubation temperature and the incubation time significantly affect the minimum inhibitory concentrations (MIC), and that these MIC depend on the antifungal or species of dermatophyte tested.In general, the studies conducted during this doctoral thesis have provided the first information about the standardization process for the antifungal susceptibility testing of dermatophytes.
Repositori URV