Collaborative Evaluation of Optimal Antifungal Susceptibility Testing Conditions for Dermatophytes

Abstract

A multicenter study was conducted to define the most suitable testing conditions for antifungal susceptibility of dermatophytes. Broth microdilution MICs of clotrimazole, itraconazole, and terbinafine were determined in three centers against 60 strains of dermatophytes. The effects of inoculum density (ca. 10 3 and 10 4 CFU/ml), incubation time (3, 7, and 14 days), endpoint criteria for MIC determination (complete [MIC-0] and prominent [MIC-2] growth inhibition), and incubation temperature (28 and 37°C) on intra-and interlaboratory agreement were analyzed. The optimal testing conditions identified were an inoculum of 10 4 CFU/ml, a temperature of incubation of 28°C, an incubation period of 7 days, and MIC-0.Dermatophytes are a group of morphologically and physiologically related molds that cause well-defined infections in vertebrates. The incidence of dermatophytoses has increased over recent years, particularly in immunocompromised patients (29,30,32,33). The choice of the proper treatment is determined by the site and extent of the infection and the species involved, as well as by the efficacy, safety profile, and kinetics of the available drugs. For localized nonextensive lesions, topical therapies with clotrimazole (CLT) are generally used. For tinea unguium, scalp ringworm, extensive infections, or skin lesions with folliculitis, systemic antifungal treatment is necessary (1,4,23,26). Oral drugs such as itraconazole (ITC) and terbinafine (TRB) are the antifungal agents currently most used to treat severe infections (4, 23). Some novel compounds, such as UR-9825, posaconazole, voriconazole, or ravuconazole, also appear to be promising candidates for the treatment of dermatophytosis (2,10,28).In the in vitro method proposed by the National Committee for Clinical Laboratory Standards (NCCLS) for testing molds (25), the dermatophytes were not included. Therefore, it is necessary to develop a reproducible standardized method for these important fungi that would lead to protocols for proper treatment. In recent years, some authors, possibly encouraged by the development of the above-mentioned reference method, have published various articles wherein several species of dermatophytes have been tested (11,27,28,34). In these works, different adaptations or modifications of the NCCLS methods have been assayed, although other techniques have also been used (3,12,15). The results obtained have been clearly contradictory in some aspects, which makes evident the need for standardization and the development of reference methods. Recently, we evaluated the activity of 11 antifungal drugs against an important number of strains of dermatophytes (n ϭ 508) by using a microdilution method (10). In that study the testing conditions adopted were an inoculum size of 10 4 CFU/ml, a temperature and time of incubation of 28°C and 7 days, respectively, and the MIC endpoint determination was 50% growth inhibition for azoles and 100% for the rest. It is unknown whether varying the conditions would have changed the results significantly....

In vitro susceptibility testing of dermatophytes isolated from pediatric cases in Nigeria against five antifungals

“…However, our results disagreed from SANTOS & HAMADA 18 and from FERNANDEZ-TORRES et al 5 . In another study FERNANDEZ-TORRES et al 4 tested 508 strains belonging to 24 species of dermatophytes against conventional (itraconazole and fluconazole) and some newer antifungal agents like voriconazole and UR-9825, with similar results. This seems to support the fact that incubating for four or seven days does not have a significant effect on the MIC readings.…”

Perfil de suscetibilidade a antifúngicos de dermatófitos isolados de pacientes com insuficiência renal crônica

“…The present results are in agreement with the findings of other investigators, who showed that the susceptibility to FCZ varies greatly from one species to another. 16,17,24 Of the topical antifungal agents, ciclopirox olamine, miconazole, piroctone olamine and tioconazole, the best results were found with tioconazole, which had the lowest geometric mean MIC and MFC values for M. gypseum, T. interdigitale and T. rubrum (Figures 2, 3 and 4). These results show that the fungicidal effect of tioconazole is greater than that of miconazole, as shown in the study by Sobue and Sekiguchi.…”

“…22 Nevertheless, not all species have the same susceptibility pattern and there is evidence that dermatophytes have become resistant to certain antimycotics. 16 Although the precise cut-off points to determine the resistance of these fungi to the different antifungal agents are not known, in this study the parameters established in the Clinical and Laboratory Standards Institute (CLSI) M38-A document for filamentous fungi were taken into consideration, which establish MIC resistance ≥ 64 μg/ml for fluconazole and MIC ≥ 8 μg/ml for itraconazole and ketoconazole. 18 Fluconazole (FCZ) was found to be the least active of all the antifungal agents evaluated (Figure 1) and this is in agreement with results published from other studies.…”

“…[7][8][9] Oral treatment with antifungal agents such as terbinafine, itraconazole, ketoconazole and fluconazole represents the treatment of choice for dermatophytoses that fail to respond to topical medication. 16 Nevertheless, the use of these medications may result in undesirable side effects in the patient. Despite its low toxicity, terbinafine may cause secondary gastrointestinal and cutaneous side effects.…”

“…[13][14][15] Oral treatment with antifungal agents such as terbinafine, itraconazole, ketoconazole and fluconazole constitutes the treatment of choice for dermatophytoses that fail to respond to topical therapy. 16 The spectrum of activity of these antifungal agents varies and this may result in treatment failure, possibly due to poor compliance by patients, lack of penetration of the drug, the bioavailability of the medication, drug interactions or resistance. 17 In vitro analysis of the antifungal activity of these drugs permits comparison between different antifungal agents and may help in selecting an effective method of treatment for patients affected by these infections.…”