Optimal growth conditions for the determination of the antifungal susceptibility of three species of dermatophytes with the use of a microdilution method

Time to Think Antifungal Resistance Increased Antifungal Resistance Exacerbates the Burden of Fungal Infections Including Resistant Dermatomycoses

Increased antifungal resistance is exacerbating the burden of invasive fungal infections, as well as potentially contributing to the increase in resistant dermatomycoses. In this commentary, we focus on antifungal drug resistance, in contrast to antibacterial resistance. We provide a brief historical perspective on the emergence of antifungal resistance and propose measures for combating this growing health concern. The increase in the incidence of invasive and cutaneous fungal infections parallels advancements in medical interventions, such as immunosuppressive drugs, to manage cancer and reduce organ rejection following transplant. A disturbing relatively new trend in antifungal resistance is the observation of several fungal species that now exhibit multidrug resistance (eg, Candida auris, Trichophyton indotineae). Increasing awareness of these multidrug-resistant species is paramount. Therefore, increased education regarding potential fungus-associated infections is needed to address awareness in the general healthcare setting, which may result in a more realistic picture of the prevalence of antifungal-resistant infections. In addition to education, increased use of diagnostic tests (eg, micro and macro conventional assays or molecular testing) should be routine for healthcare providers facing an unknown fungal infection. Two critical barriers that affect the low rates for Antifungal Susceptibility Testing (AST) are low (or a lack of) sufficient insurance reimbursement rates and the low number of qualified laboratories with the capacity to perform AST. The ultimate aim is to improve the quality of patient care through fungal identification, diagnosis, and, where appropriate, susceptibility testing. Here we propose an all-encompassing call to action to address this emerging challenge.

Antifungal Susceptibility Testing: A Primer for Clinicians

Clinicians treating patients with fungal infections may turn to susceptibility testing to obtain information regarding the activity of different antifungals against a specific fungus that has been cultured. These results may then be used to make decisions regarding a patient's therapy. However, for many fungal species that are capable of causing invasive infections, clinical breakpoints have not been established. Thus, interpretations of susceptible or resistant cannot be provided by clinical laboratories, and this is especially true for many molds capable of causing severe mycoses. The purpose of this review is to provide an overview of susceptibility testing for clinicians, including the methods used to perform these assays, their limitations, how clinical breakpoints are established, and how the results may be put into context in the absence of interpretive criteria. Examples of when susceptibility testing is not warranted are also provided.

Antifungal susceptibility testing of dermatophytes: Development and evaluation of an optimised broth microdilution method

BACKGROUND

Dermatophytosis is one of the most common infections affecting 3%-17% of the population. Resistance to antifungals so far was not of concern in the therapeutic management. However, recent reports of terbinafine-resistant strains in several countries are worrisome making antifungal susceptibility testing inevitable.

OBJECTIVES

We aimed to develop and evaluate an optimised broth microdilution assay for antifungal drug susceptibility testing of dermatophytes.

METHODS

We first studied the effect of different inocula, incubation temperatures and incubation times to establish an optimised assay. Subsequently, we tested 79 clinical strains of 11 dermatophyte species with 13 antifungals.

RESULTS

We found inoculating with 0.5-5 × 10⁴ colony forming units (CFU) and incubating at 29°C ± 1°C for 4 days to be appropriate. Terbinafine was the most active antifungal agent with minimum inhibitory concentration (MIC) values ≤ 0.06 µg/mL, expect for one resistant T mentagrophytes strain, which was isolated from an Indian patient. Also, a majority of MICs of other antifungals that are commonly used to treat dermatophytosis were low, except those of fluconazole. Fluconazole MICs do not correlate with the good efficacy in the clinical management.

CONCLUSIONS

Our assay enables fast and reliable susceptibility testing of dermatophytes with a large panel of different antifungals. This helps to improve the therapeutic management of dermatophytosis by detecting resistant strains.

Comparison of Four Methods for the in vitro Susceptibility Testing of Dermatophytes

Objectives

Infections caused by dermatophytes affect a high percentage of the population. Antifungal susceptibility testing (AST) can offer useful information about the susceptibility profiles of the pathogens as well as the concomitant documentation of the appropriate treatment. However, the slow growth rate of these fungi and their poor sporulation are factors that can delay and affect the performance of the AST. The proposed methods by the CLSI or the EUCAST are both laborious for the everyday routine. There are alternative applications which propose the use of an inoculum, consisting of a conidia-mycelium mixture or even plain mycelia, as well as the use of resazurin in order to facilitate the reading. The aim of this study was to compare these approaches to the EUCAST method and evaluate their performance.

Methods

Three alternative methods were compared to the EUCAST proposed methodology for conidia forming molds. The last was defined as the reference method. The methods under evaluation were (a) a fragmented mycelia method, (b) the EUCAST method with the addition of resazurin sodium salt solution and (c) the fragmented mycelia method with the addition of resazurin sodium salt solution. Twenty-two isolates (8 Trichophyton interdigitale, 8 T. rubrum, and 6 Microsporum canis) were tested against the antifungal agents of griseofulvin, terbinafine, fluconazole, and itraconazole.

Results

The essential agreement between the methods was calculated in percentages and a statistical analysis of the results was performed. Data evaluation revealed sufficient overall agreement of the methods with the addition of resazurin to the initial “uncolored” methods (98.9 and 97.5% for the EUCAST and the fragmented mycelia methods, respectively). The fragmented mycelia method exhibited a relatively sufficient overall agreement in comparison to the EUCAST method (90%) and not a satisfactory correlation, probably as a result of various issues of standardization.

Conclusion

The EUCAST method was found to be the more reliable one, whereas the addition of resazurin sodium salt solution facilitates the reading and provides a reliable and objective evaluation. The fragmented mycelia method could serve as an alternative that should be applied only in cases of poor or no sporulating dermatophytes.

Therapy and Antifungal Susceptibility Profile of Microsporum canis

Microsporum canis is a worldwide diffused zoophilic dermatophyte which causes clinical conditions often characterised by multifocal alopecia, scaling, and circular lesions in many animal species, including humans. A large variety of oral and topical antifungal protocols is available for treating M. canis infection. However, the efficacy of these drugs and treatment protocols is variable, with treatment failure up to 40% of patients possibly due to resistance phenomena. The lack of standardised reference methods for evaluating the antifungal susceptibility of M. canis represents a major hindrance in assessing microbiological resistance in unresponsive clinical cases. Therefore, data about conventional therapy against M. canis and the protocols employed to test the antifungal activity of the most commonly employed drugs (i.e., azoles, polyenes, allylamines, and griseofulvin) have been summarised herein. This article focuses on technical parameters used for antifungal susceptibility tests, their effects on the minimum inhibitory concentration value, as well as their clinical implications.

In vitro model of infected stratum corneum for the efficacy evaluation of poloxamer 407-based formulations of ciclopirox olamine against Trichophyton rubrum as well as differential scanning calorimetry and stability studies

Superficial fungal skin infections are a common disease and concern 20-25% of the world's population with the dermatophyte Trichophyton rubrum being the main trigger. Due to autoinoculation, fungal skin infections of the feet (tinea pedis) often occur simultaneously with fungal nail infections (onychomycosis). Therefore, the overall objective was the development and characterisation of poloxamer 407-based formulations with the antimycotic active ingredient ciclopirox olamine (CPX) for simultaneous antifungal therapy. The formulations consisted of poloxamer 407, water, isopropyl alcohol, propylene glycol and medium chain triglycerides in given ratios. The in vitro antifungal efficacy against T. rubrum was tested in a novel in vitro model of infected stratum corneum in comparison to a marketed semi-solid formulation containing 1% (w/w) ciclopirox olamine and a marketed nail lacquer containing 8% ciclopirox. Several liquid poloxamer 407-based formulations with only 1% CPX completely inhibited fungal growth after 6 days of incubation, whereas the marketed semi-solid formulation did not inhibit fungal growth. Differential scanning calorimetry studies revealing the interaction between the formulations and the SC showed that increasing isopropyl alcohol/propylene glycol concentrations as well as increasing CPX concentrations caused increasing endothermic transition shifts. Moreover, stability studies at 30 °C exhibited only a slight decrease of the CPX amount after 12 months of storage. Each formulation contained >90% of the initial CPX concentration after termination of the stability studies.

Development and Application of a High-Throughput Screening Method to Evaluate Antifungal Activity against Trichophyton tonsurans

There exist relatively few drug classes on the market to treat dermatophyte infections. This investigation was designed to develop and validate high-throughput methodology for screening and confirmation of chemicals for activity against Trichophyton tonsurans. Growth characteristics were examined on two platforms (96- and 384-well) in three media at eight spore concentrations over a period of up to 120 h. Microspectrophotometry was used to automate plate reads. The 384-well platform was used to screen more than 7000 compounds from six chemical libraries. Z-scores for optical density relative to positive growth controls were used to flag compounds of interest and activity confirmed in separate assays. The final conditions selected for both screening and confirmation with minimum inhibitory concentration (MIC) determination were growth for 48 h at 32 °C in SabDex with 1 × 10(4) spores per reaction. Sensitivity and specificity averaged 99.2% (range, 95.2%-100%) and 99.8% (range, 99.1%-100%), respectively. MICs for known antifungals were similar to those reported by others using Clinical and Laboratory Standards Institute methods. Several novel compound classes were identified to have activity against T. tonsurans with potency comparable to known antifungals. A robust, reproducible assay is described that permits high-throughput screening in T. tonsurans.

Progressive development in experimental models of transungual drug delivery of anti-fungal agents

Pre-clinical development comprises of different procedures that relate drug discovery in the laboratory for commencement of human clinical trials. Pre-clinical studies can be designed to recognize a lead candidate from a list to develop the procedure for scale-up, to choose the unsurpassed formulation, to determine the frequency, and duration of exposure; and eventually make the foundation of the anticipated clinical trial design. The foremost aim in the pharmaceutical research and industry is the claim of drug product quality throughout a drug's life cycle. The particulars of the pre-clinical development process for different candidates may vary; however, all have some common features. Typically in vitro, in vivo or ex vivo studies are elements of pre-clinical studies. Human pharmacokinetic in vivo studies are often supposed to serve as the 'gold standard' to assess product performance. On the other hand, when this general assumption is revisited, it appears that in vitro studies are occasionally better than in vivo studies in assessing dosage forms. The present review is compendious of different such models or approaches that can be used for designing and evaluation of formulations for nail delivery with special reference to anti-fungal agents.

Susceptibility of clinically important dermatophytes against statins and different statin-antifungal combinations

The investigation of the antifungal activities of drugs whose primary activities are not related to their antimicrobial potential is in the current forefront of research. Statin compounds, which are routinely used as cholesterol-lowering drugs, may also exert direct antimicrobial effects. In this study, the in vitro antifungal activities of various statins (lovastatin, simvastatin, fluvastatin, atorvastatin, rosuvastatin and pravastatin) were examined against one isolate each of four dermatophyte species (Trichophyton mentagrophytes, Trichophyton rubrum, Microsporum canis and Microsporum gypseum). Basically, statins were effective in inhibiting all dermatophyte studied, but were particularly active against M. canis and T. mentagrophytes. Fluvastatin and simvastatin were active against all of the tested fungi causing a complete inhibition of their growth at very low concentrations (6.25-12.5 μg/ml). Lovastatin and rosuvastatin had inhibitory effects at higher concentrations (25-128 μg/ml), while atorvastatin and pravastatin proved the less effective. The in vitro interactions between statins and different antifungals (ketoconazole, itraconazole, fluconazole, amphotericin B, nystatin, griseofulvin, terbinafine and primycin) were also investigated using a standard chequerboard broth microdilution method. Synergetic interactions were observed in several cases, most of them were noticed when statins were combined with terbinafine and the different azoles. Some combinations were particularly active (ketoconazole-simvastatin or terbinafine-simvastatin), as they were found to exert synergistic effect against all of the investigated isolates. The other antifungals showed synergistic interactions with statins in only certain cases. These results suggest that statins exert substantial antifungal effects against dermatophyte fungi and they should be promising components in a combination therapy as they can act synergistically with a number of clinically used antifungal agents.

Evaluation of Antifungal Efficacy in an Optimized Animal Model ofTrichophytonmentagrophytes-Dermatophytosis

Dermatophytoses are known to cause considerable discomfort, cosmetic problems and financial loss that have been recognized as a significant health concern worldwide. Since currently available antifungal agents have limitations in their efficacy, new agents are being developed. This study was undertaken to optimize an in vivo model of experimental dermatophytosis for evaluation of the efficacy of antifungal compounds. Guinea pigs were infected with different inocula of T. mentagrophytes to establish dermatophytosis. The optimal conditions for dermatophytosis in guinea pigs were found to be an inoculum size of 1 x 10(7) fungal cells applied on abraded skin. After optimization, animals were treated with oral or topical formulations of terbinafine. The optimized guinea pig model was found to be highly reproducible, and useful in the primary screening and evaluation of the anti-dermatophytic efficacy of topical and oral formulations of antifungal agents.

Infected nail plate model made of human hair keratin for evaluating the efficacy of different topical antifungal formulations against Trichophyton rubrum in vitro

A novel model of infected nail plate for testing the efficacy of topical antifungal formulations has been developed. This model utilized keratin film made of human hair keratin as a nail plate model. Subsequent to infection by Trichophyton rubrum, the common causative agent of onychomycosis, keratin films as infected nail plate models were treated with selected topical formulations, that is cream, gel, and nail lacquer. Bovine hoof was compared to keratin film. In contrast to the common antifungal susceptibility test, the antifungal drugs tested were applied as ready-to-use formulations because the vehicle may modify and control the drug action both in vitro and in vivo. Extrapolating the potency of an antifungal drug from an in vitro susceptibility test only would not be representative of the in vivo situation since these drugs are applied as ready-to-use formulations, for example as a nail lacquer. Although terbinafine has been acknowledged to be the most effective antifungal agent against T. rubrum, its antifungal efficacy was improved by its incorporation into an optimal formulation. Different gels proved superior to cream. Therefore, this study is able to discriminate between efficacies of different topical antifungal formulations based on their activities against T. rubrum.

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

The antifungal activities of itraconazole, ketoconazole, fluconazole, terbinafine and griseofulvin were tested by broth microdilution methods against 71 isolates of dermatophytes isolated from Nigerian children. Most drugs were very active against all the dermatophytes and the MIC 90 ranged from 0.03 to 8.0 µg/mL. This appears to be the first documented data on the antifungal susceptibility testing of isolates of dermatophytes from Nigerian children.

In vitro antifungal susceptibility patterns of dermatophyte strains causing tinea unguium

BACKGROUND

Dermatophytes are the major responsible organisms in onychomycosis. Although recent antifungal agents have high success rates in treating this condition, lack of clinical response may occur in 20%. Antifungal drug resistance may be one of the causes of treatment failure. The need for in vitro antifungal drug resistance in daily practice is still under discussion.

OBJECTIVE

We aimed to determine the in vitro susceptibility patterns of dermatophytes causing onychomycosis, against the traditionally available systemic antifungal agents terbinafine, itraconazole and fluconazole.

METHODS

In total, 100 otherwise healthy patients with suspected onychomycosis were included. Nail clippings were cultured on Sabouraud dexrose agar, mycobiotic agar and dermatophyte test medium. Antifungal susceptibility tests were carried out, mainly following The National Committee for Clinical and Laboratory Standards (M38-P) protocol standard for filamentous fungi. Different concentrations of terbinafine (0.008-8 microg/mL), itraconazole (0.015-16 microg/mL) and fluconazole (0.06-64 microg/mL) were tested. Minimum inhibitory concentration end-point determination was chosen as 100% growth inhibition for terbinafine and 80% for azoles.

RESULTS

Of the 100 nail samples, 43% grew dermatophytes. The main causative organism was Trichophyton rubrum (91%) followed by Trichophyton mentagrophytes (9%). Terbinafine had the lowest minimum inhibitory concentration (0.008 microg/mL) followed by itraconazole. Fluconazole showed the greatest variation in minimum inhibitory concentration (0.03-2 microg/mL) and had different susceptibility patterns for the two species.

CONCLUSIONS

Of the three antifungals tested, terbinafine had the most potent in vitro antifungal activity against dermatophytes. Antifungal susceptibility tests would be useful to screen antifungal-resistant dermatophyte strains.

In vitro activities of four antifungal drugs against Trichophyton rubrum isolates exhibiting resistance to fluconazole

Thirty-two clinical isolates of Trichophyton rubrum exhibiting resistance to fluconazole [minimum inhibitory concentrations (MICs) > or = 64 microg ml(-1)] were selected to test the antifungal activity of ketoconazole, itraconazole, griseofulvin and terbinafine. We followed the guidelines of the National Committee for Clinical Laboratory Standards for testing filamentous fungi. The strains Candida parapsilosis (ATCC 22019), Candida krusei (ATCC 6258), T. rubrum (ATCC 40051) and Trichophyton mentagrophytes (ATCC 40004) were included for quality control. The microdilution plates were incubated at 28 degrees C and were read visually after 7 days of incubation and endpoint determination readings were performed visually. The MIC ranges for the four antifungals were: 0.0625-2 microg ml(-1) for ketoconazole, 0.25-2.0 microg ml(-1) for griseofulvin, < or =0.031-1.0 microg ml(-1) for itraconazole and < or =0.031 microg ml(-1) for terbinafine (for all tested isolates). Terbinafine was the most potent drug against T. rubrum, in vitro, followed by itraconazole, ketoconazole and griseofulvin. Much work is still needed to correlate the MICs of these drugs with clinical outcomes to develop interpretative breakpoints for T. rubrum and other dermatophytes.

Evaluation of susceptibility of Trichophyton mentagrophytes and Trichophyton rubrum clinical isolates to antifungal drugs using a modified CLSI microdilution method (M38-A)

Onychomycosis is a common adult human mycosis, and dermatophytes of the Trichophyton genera are the most common causative agent. Many antimycotic agents are safe and highly effective for the treatment of dermatophytosis, and are available for clinical practice. Successful treatment depends on the ability of antifungal drugs to eradicate the fungal isolates. The aim of this work was to determine the MICs of four antifungal drugs (fluconazole, itraconazole, terbinafine and griseofulvin) recognized for ungual dermatophytosis treatment caused by Trichophyton species, especially Trichophyton mentagrophytes and Trichophyton rubrum. MICs were determined using a broth microdilution method in accordance with Clinical and Laboratory Standards Institute approved standard M38-A with some modifications, such as an incubation temperature of 28 °C, an incubation time of 7 days and inocula constituted of only microconidia. The results showed that the activities of terbinafine and itraconazole were significantly higher (MICs of <0.007–0.031 and 0.015–0.25 μg ml−1, respectively) than other tested agents. All isolates had reduced susceptibility to fluconazole (1–64 μg ml−1). The MIC of griseofulvin varied among strains (MICs of 0.062–1 μg ml−1). The parameters adopted to perform susceptibility testing of T. rubrum and T. mentagrophytes to antifungal agents appeared to be suitable and reliable, and could contribute to the possible development of a standard protocol.

In vitro activities of miltefosine and two novel antifungal biscationic salts against a panel of 77 dermatophytes

The susceptibilities of 77 dermatophytes to miltefosine (MI), 1,12-bis(4-pentylpyridinium)dodecane (PYR), 1,12-bis(tributylammonium)dodecane (AM), itraconazole (ITC), terbinafine (TRB), and butenafine (BTF) were compared. Geometric mean MICs of TRB, BTF, ITC, MI, PYR, and AM were 0.039, 0.059, 1.718, 0.671, 6.006, and 4.771 microg/ml, respectively. MI was more active than ITC (P < 0.001).

Species distribution and antifungal susceptibilities of dermatophytes during a one year period at a university hospital in Turkey

Dermatophyte infections have been considered to be a major public health problem in many parts of the world. The aim of this study was to determine the causative agents of dermatophytoses and their antifungal susceptibilities in a Turkish University Hospital, west of Turkey. A total of 926 patients suspected to have dermatophytic lesions were examined over a period of 1 year (2001-2002). Samples collected from skin, hair and nails were submitted to direct microscopical examination using KOH and Calcofluor white stain, cultured on Sabouraud dextrose agar and Mycosel agar. The prevalence of dermatophytoses was 7.34% (68/926). Trichophyton rubrum was the most frequent dermatophyte isolated (56%) followed by T. mentagrophytes (38%), T. violaceum (1.5%), T. verrucosum (1.5%), Microsporum canis (1.5%) and Epidermophyton floccosum (1.5%). Tinea pedis (47%) was the most common type of infection, followed by tinea unguium (29%), tinea inguinalis (15%), tinea corporis (7.4%) and tinea capitis (1.6%). Secondary, we have tested 68 strains of dermatophytes against four antifungal agents following mainly the National Committee for Clinical Laboratory Standards M38-P standard for filamentous fungi. In general, all antifungals were shown to be highly effective and itraconazole and naftifine appeared more active than ketoconazole and oxiconazole.

Evaluation of microdilution and disk diffusion methods for antifungal susceptibility testing of dermatophytes

A total of 63 dermatophyte strains belonging to 6 species (Trichophyton rubrum (16), T. mentagrophytes (16), T. tonsurans (20), T. violaceum (2), Microsporum canis (7), and Epidermophyton floccosum (2)) were tested for their in vitro susceptibility to a range of antifungal drugs using disk diffusion and Clinical Laboratory Standards Institute M38-A (CLSI, formerly NCCLS) broth microdilution methods. The antifungals used were ciclopirox (CIC), terbinafine (TER), griseofulvin (GRE), fluconazole (FLC), itraconazole (ITR), posaconazole (POS), and ravuconazole (RAV). In the broth microdilution assay terbinafine was found to have the highest activity followed by ravuconazole, posaconazole, ciclopirox, itraconazole, griseofulvin and fluconazole. In the disk diffusion assay terbinafine produced the largest inhibition zone diameters (IZDs) on Dermasel agar media followed by ravuconazole, griseofulvin, posaconazole, and itraconazole. A significant correlation was not observed between the minimum inhibitory concentrations (MICs) and IZDs, but some correlations were observed for POS, RAV, and TER (correlation coefficients r=-0.507, -0.249, -0.267, P<0.05, respectively). MICs obtained by the microdilution method with ITR and GRE did not correlate with IZDs obtained in disk diffusion assays in this study. The ciclopirox (20 microg/disk) and fluconazole (25 microg/disk) did not produce well defined inhibition zone diameters on Dermasel agar medium.

Voriconazole susceptibilities of dermatophyte isolates obtained from a worldwide tinea capitis clinical trial

In this study, the voriconazole susceptibilities of dermatophyte isolates obtained from a worldwide tinea capitis trial were compared to their susceptibilities to fluconazole and griseofulvin. The MIC ranges of voriconazole, fluconazole, and griseofulvin, were 0.002 to 0.06 microg/ml, 0.25 to 32 microg/ml, and 0.125 to 2.0 microg/ml, respectively.

Interlaboratory study of quality control isolates for a broth microdilution method (modified CLSI M38-A) for testing susceptibilities of dermatophytes to antifungals

The Clinical and Laboratory Standards Institute (CLSI; formerly National Committee for Clinical Laboratory Standards, or NCCLS) M38-A standard for the susceptibility testing of filamentous fungi does not specifically address the testing of dermatophytes. In 2003, a multicenter study investigated the reproducibility of the microdilution method developed at the Center for Medical Mycology, Cleveland, Ohio, for testing the susceptibility of dermatophytes. Data from that study supported the introduction of this method for testing dermatophytes in the future version of the CLSI M38-A standard. In order for the method to be accepted by CLSI, appropriate quality control isolates needed to be identified. To that end, an interlaboratory study, involving the original six laboratories plus two additional sites, was conducted to evaluate potential candidates for quality control isolates. These candidate strains included five Trichophyton rubrum strains known to have elevated MICs to terbinafine and five Trichophyton mentagrophytes strains. Antifungal agents tested included ciclopirox, fluconazole, griseofulvin, itraconazole, posaconazole, terbinafine, and voriconazole. Based on the data generated, two quality control isolates, one T. rubrum isolate and one T. mentagrophytes isolate, were identified and submitted to the American Type Culture Collection (ATCC) for inclusion as reference strains. Ranges encompassing 95.2 to 97.9% of all data points for all seven drugs were established.

Evaluation of peptone glucose fluconazole agar as a selective medium for rapid and enhanced isolation of Aspergillus fumigatus from the respiratory tract of bronchopulmonary aspergillosis patients colonized by Candida albicans

We have reported earlier that Aspergillus fumigatus is inhibited in vitro by Candida albicans which also interferes in its isolation from sputum experimentally seeded with predetermined graded inocula of the two fungi. It was further shown that this interference was neutralized by employing peptone glucose agar with incorporation of fluconazole which is more inhibitory to C. albicans than to A. fumigatus. This communication embodies the results of evaluation of peptone glucose fluconazole agar (PGFA) as a selective culture medium for rapid and enhanced isolation of A. fumigatus from sputum of patients clinically suspected of aspergillosis with C. albicans colonization in the respiratory tract. Of the 23 sputum specimens and one broncho-alveolar lavage collected from 15 suspected aspergillosis patients, A. fumigatus was isolated from all (100%) on PGFA as against only 19 specimens (79%) that proved to be positive on the control PGA medium (P<0.05). The greater efficacy of PGFA than that of PGA was further evident from the 2-fold higher A. fumigatus mean colony count (8.2+/-1.87) on the former medium than on the latter (3.7+/-1.00), and this difference was found to be statistically significant (P<0.05). Besides, A. fumigatus colonies were macroscopically recognizable within 2-3 days on PGFA at 28 degrees C in strong contrast to 5-7 days required on PGA. Based upon these observations, PGFA is recommended for wider application as a selective medium for rapid and enhanced recovery of A. fumigatus from sputum of patients clinically suspected of aspergillosis with C. albicans colonization in their respiratory tract.

Dermatophytes growth curve and in vitro susceptibility test: a broth micro-titration method

The introduction of systemic antifungal drugs which act upon different targets is the main issue of the in vivo antifungal resistance control. Different factors, such as growth curve phase, quality of the specimen, quantity of the inoculum, temperature, pH, culture medium composition, incubation duration and solvent, are believed important factors affecting minimum inhibitory concentration (MIC) value to most of the antifungal agents. We assayed an in vitro susceptibility test with 40 isolates of dermatophytes: Microsporum canis, Trichophyton rubrum, Trichophyton mentagrophytes and Epidermophyton floccosum against griseofulvin, fluconazole, itraconazole and terbinafine, using the guidelines of the M38-P document approved by the NCCLS. We determined the growth curves, to estimate the specific growth rate (mu max) and the generation time (G) of each dermatophyte, using dry weight and spectrophotometry methods. We demonstrate that, at 192 h, all fungi tested had a constant growth curve and we considered this as the optimal time for MIC determination. Terbinafine, griseofulvin and itraconazole possessed the highest antifungal activity against the four groups of dermatophytes studied. Fluconazole demonstrated no efficacy. Our MIC results differ from other authors and this difference is due to the timing of the MIC determination based on the growth curve of each fungi tested.

Evaluation of broth microdilution antifungal susceptibility testing conditions for Trichophyton rubrum

Fifty clinical isolates of Trichophyton rubrum were selected to test with ketoconazole, fluconazole, itraconazole, griseofulvin, and terbinafine by following the National Committee for Clinical Laboratory Standards susceptibility testing guidelines for filamentous fungi (M38-A). In addition, other susceptibility testing conditions were evaluated: (i) three medium formulations including RPMI 1640 (standard medium), McVeigh & Morton (MVM), and Sabouraud dextrose broth (SDB); (ii) two incubation temperatures (28 and 35 degrees C); and (iii) three incubation periods (4, 7, and 10 days). The strains Candida parapsilosis (ATCC 22019), Candida krusei (ATCC 6258), T. rubrum (ATCC 40051), and Trichophyton mentagrophytes (ATCC 40004) were included as quality controls. All isolates produced clearly detectable growth only after 7 days of incubation. MICs were significantly independent of the incubation temperature (28 or 35 degrees C) (P < 0.05). Different incubation periods resulted in MICs which were consistently different for each medium when azoles and griseofulvin were tested (P < 0.05). MICs obtained from different media at the same incubation time for the same isolate were significantly different when azoles and griseofulvin were tested (P < 0.05). MICs were consistently higher (usually 1 to 2 dilutions) with RPMI than with MVM or SDB (P < 0.05). When terbinafine was tested, no parameter had any influence on MICs (P < 0.05). RPMI standard medium appears to be a suitable testing medium for determining the MICs for T. rubrum. MICs obtained at different incubation times need to be correlated with clinical outcome to demonstrate which time has better reliability.

In vitro susceptibility testing of Microsporum gypseum isolated from healthy cattle and soil samples against itraconazole, terbinafine, fluconazole and topical veterinarian drugs

The present study evaluated in vitro susceptibility testing of dermatophytes isolates from healthy cattle and soil samples against three antifungal agents and three topical veterinarian drugs. Itraconazole and terbinafine showed a higher in vitro fungicidal activity than fluconazole. The veterinarian drugs LEPECID and iodine 5% were more active in vitro than the UNGUENTO spray. All drugs showed fungicidal activity against Microsporum gypseum, and they may be considered as efficient agents for the topical treatment of dermatophytoses in cattle.

In vitroactivities of posaconazole, ravuconazole, terbinafine, itraconazole and fluconazole against dermatophyte, yeast and non-dermatophyte species

The in vitro activities of two new triazole antifungal agents with broad-spectrum antifungal activity, posaconazole and ravuconazole, were compared with those of three well-established antifungal agents, terbinafine, itraconazole and fluconazole, against 184 clinical isolates. These included 129 dermatophyte isolates (twelve species), 25 yeast isolates (five species) and 28 non-dermatophyte isolates (nine species). In vitro testing was conducted using microdilution plates with RPMI 1640 and National Committee for Clinical Laboratory Standards (NCCLS) guidelines (M27-38P) were followed, except for the preparation of the dermatophyte inoculum. Both posaconazole and ravuconazole showed similar broad-spectrum activity against dermatophyte, yeast and non-dermatophyte species. Mean inhibitory concentrations (MIC) at which 90% [MIC90] of the isolates were inhibited by posaconazole and ravuconazole were 0.25 and 0.5 microg/ml for dermatophytes, 0.5 and 0.25 microg/ml for yeasts, and >4 and 8 microg/ml for non-dermatophytes. The MIC ranges against Trichophyton (six species), Microsporum (five species) and Epidermophyton flocossum were: posaconazole (0.007-1.0/0.007-0.25/0.007-1.0 microg/ml), ravuconazole (0.015-8.0/0.015-1.0/0.015-1.0 microg/ml), itraconazole (0.015- >8.0/0.015-0.5/ 0.015-8.0 microg/ml), fluconazole (0.125- >64.0/4.0 >64.0/0.5-64.0 microg/ml) and terbinafine (0.003 >2.0/0.007-2.0/0.007 >2.0 microg/ml). Overall ranking of the antifungal activity of the five antifungal agents was: terbinafine > posaconazole > ravuconazole > itraconazole > fluconazole, for dermatophytes; ravuconazole > posaconazole > itraconazole > fluconazole > terbinafine, against yeasts; and posaconazole > ravuconazole > terbinafine > itraconazole > fluconazole, for non-dermatophytes.

In vitro Antifungal Activity of Sertaconazole Compared with Nine Other Drugs against 250 Clinical Isolates of Dermatophytes and Scopulariopsis brevicaulis

We have tested 250 strains belonging to 15 species of clinically important dermatophytes and Scopulariopsis against ten antifungal drugs using an agar diffusion method (NeoSensitabstrade mark, Rosco, Taastrup, Denmark). Some of the experimental factors were adapted to dermatophyte development, such as temperature (28 vs. 35 degrees C) and time of incubation (2-5 days vs. 21-74 h). The antifungals used are itraconazole, ketoconazole, miconazole, clotrimazole, sertaconazole, terbinafine, tioconazole, fluconazole, isoconazole and econazole. Except for fluconazole, all the drugs tested have shown to be highly effective, especially sertaconazole and terbinafine. Percentages of susceptibility ranged between 94% for terbinafine, 87.6% for sertaconazole and 86.4% clotrimazole; 81.6% econazole; 42.8% fluconazole; 57.2% isoconazole; 78.4% itraconazole; 74.4% ketoconazole; 73.3% miconazole, and 85.2% for tioconazole. Percentages of resistance were similar between sertaconazole and terbinafine (4%) but in contrast to the 48% obtained for fluconazole.

Intra- and interlaboratory study of a method for testing the antifungal susceptibilities of dermatophytes

The National Committee for Clinical Laboratory Standards (NCCLS) M38-A standard for the susceptibility testing of conidium-forming filamentous fungi does not explicitly address the testing of dermatophytes. This multicenter study, involving six laboratories, investigated the MIC reproducibility of seven antifungal agents tested against 25 dermatophyte isolates (5 blinded pairs of five dermatophyte species per site for a total of 300 tests), using the method of dermatophyte testing developed at the Center for Medical Mycology, Cleveland, Ohio. The dermatophytes tested included Trichophyton rubrum, Trichophyton mentagrophytes, Trichophyton tonsurans, Epidermophyton floccosum, and Microsporum canis. Seven antifungals with activity against dermatophytes were tested, including ciclopirox, fluconazole, griseofulvin, itraconazole, posaconazole, terbinafine, and voriconazole. Interlaboratory MICs for all isolates were in 92 to 100% agreement at a visual endpoint reading of 50% inhibition as compared to the growth control and 88 to 99% agreement at a visual endpoint reading of 80% inhibition as compared to the growth control. Intralaboratory MICs between blinded pairs were in 97% agreement at a visual endpoint reading of 50% inhibition as compared to the growth control and 96% agreement at a visual endpoint reading of 80% inhibition as compared to the growth control. Data from this study support consideration of this method as an amendment to the NCCLS M38-A standard for the testing of dermatophytes.

In vitro susceptibility testing of dermatophytes: comparison of disk diffusion and reference broth dilution methods

A total of 56 strains belonging to 4 species of dermatophytes were tested against 10 antifungal drugs by using a modification of the NCCLS (M38-P) standard for filamentous fungi. The minimum inhibitory concentration (MIC) values obtained using the dilution method were compared with the diameters of growth inhibition zones using the disk diffusion method. The antifungals used were itraconazole, fluconazole, ketoconazole, miconazole, sulconazole, oxiconazole, bifonazole, griseofulvin, ciclopiroxolamine, and terbinafine. Relative to the other agents tested, terbinafine possessed the highest antifungal activity against all of the dermatophytes. In contrast, fluconazole was the least active drug. An increase of MIC values was accompanied by a decrease of growth inhibition zone diameter. The disk diffusion method of fungal susceptibility assessment yields data consistent with results obtained from the dilution method. The study suggests the potential value of the disk diffusion method as a convenient alternative method for testing the susceptibilities of dermatophytes.

[In vitro activity of voriconazole and three other antifungal agents against dermatophytes]

INTRODUCTION

The increase in infections due to dermatophytes in recent years led us to study the effectiveness of new antifungal formulations against these microorganisms.

METHODS

The in vitro activity of a new antifungal agent, voriconazole, was compared with three other antifungal agents, itraconazole, fluconazole and terbinafine, against 120 dermatophytes belonging to four species (61 Trichophyton mentagrophytes, 34 Microsporum canis, 13 M. gypseum and 12 T. rubrum). A broth microdilution method was used following the recommendations of the NCCLS document M38-P with some modifications.

RESULTS

Terbinafine was the most active agent against the dermatophytes studied (MIC90 < or = 0.03 mg/ml), followed by voriconazole (MIC90, 0.25 micro g/ml) and itraconazole (MIC90, 0.5 micro g/ml). Fluconazole was the least active antifungal agent. The most susceptible species was M. canis.

CONCLUSIONS

Voriconazole was found to have effective activity against dermatophytes.

Comparison of in vitro activities of 17 antifungal drugs against a panel of 20 dermatophytes by using a microdilution assay

The in vitro activities of 17 antifungal drugs against a panel of 20 dermatophytes comprising 6 different species were determined using a microdilution assay according to the NCCLS M38-P method with some modifications. Terbinafine was the most potent systemic drug while tolnaftate and amorolfine were the most active topical agents.

In vitro susceptibility testing of ciclopirox, terbinafine, ketoconazole and itraconazole against dermatophytes and nondermatophytes, and in vitro evaluation of combination antifungal activity

BACKGROUND

With the development of newer antifungal agents with activity against both yeasts and filamentous fungi, there is an increased need to develop and standardize in vitro assays that will evaluate the activity of antimycotics against filamentous fungi. In vitro analysis of antifungal activity of these agents would also allow for the comparison between different antimycotics, which in turn may clarify the reasons for lack of clinical response or serve as an effective therapy for patients with chronic infection.

OBJECTIVES

To determine the in vitro susceptibility of fungal organisms to ciclopirox, terbinafine, ketoconazole and itraconazole and to evaluate the in vitro activity and mode of interaction of ciclopirox in combination with either terbinafine or itraconazole.

MATERIALS AND METHODS

In the minimum inhibitory concentration (MIC) study 133 strains were evaluated, including dermatophytes (110 strains; 98 from Trichophyton spp.), Candida spp. (14 strains) and nondermatophyte moulds (nine strains). In vitro susceptibility testing was conducted in microbroth dilutions based on the National Committee for Clinical Laboratory Standards (NCCLS) M27-A proposed standard. The testing MIC ranges were 0.003-2 microg mL-1 for ciclopirox and terbinafine, and 0.06-32 microg mL-1 for itraconazole and ketoconazole. For inoculum preparation, dermatophytes were grown on Heinz oatmeal cereal agar slants. Inoculum suspensions of dermatophytes were diluted in RPMI 1640 (Sigma-Aldrich) with the desired final concentration being 2-5 x 103 c.f.u. mL-1. Once inoculated, the microdilution plates were set up according to the NCCLS M27-A method, incubated at 35 degrees C, and read visually following 7 days of incubation. For azole agents, the MIC was the lowest concentration showing 80% growth inhibition; for terbinafine and ciclopirox, the MIC was the lowest concentration showing 100% growth inhibition. In the synergy studies, 29 strains from nondermatophyte species were evaluated using a checkerboard microdilution method. The concentrations tested were: 0 and 0.06-32 microg mL-1 for itraconazole, and 0 and 0.003-4 microg mL-1 for both terbinafine and ciclopirox. Modes of interaction between drugs were classified as synergism, additivism, antagonism or indifference based on fractional inhibitory concentration index values (FIC index). Synergism was defined as an FIC index of < or = 0.50, additivity as an FIC index of < or = 1.0, and antagonism as an FIC index of > or = 2.0. The drug combination was interpreted as indifferent if neither of the drugs had any visible effect on the presence of the other drug.

RESULTS

In the MIC study, the dermatophyte MIC values (microg mL-1) (mean +/- SEM) were: ciclopirox (0.04 +/- 0.02), terbinafine (0.04 +/- 0.23), itraconazole (2.28 +/- 7.42) and ketoconazole (0.83 +/- 1.99). The yeast MIC values (microg mL-1) (mean +/- SEM) were: ciclopirox (0.05 +/- 0.02), terbinafine (1.77 +/- 0.58), itraconazole (0.18 +/- 0.27) and ketoconazole (0.56 +/- 0.60). The non-dermatophyte fungi MIC values (microg mL-1) (mean +/- SEM) were: ciclopirox (1.04 +/- 2.62), terbinafine (1.04 +/- 0.95), itraconazole (17.87 +/- 16.75) and ketoconazole (10.69 +/- 13.09). In the synergy study, with ciclopirox in combination with terbinafine, mainly a synergistic or additive reaction was observed; there were no cases of antagonism. For ciclopirox in combination with itraconazole, there were some instances of additivism or synergism, with indifference in the majority of instances; there were no cases of antagonism.

CONCLUSIONS

In vitro susceptibility testing indicates that ciclopirox may have a broad antimicrobial profile including dermatophytes, yeasts and other nondermatophytes. Terbinafine is extremely potent against dermatophytes. In vitro evaluation of activity of ciclopirox and terbinafine suggests many instances of synergy or additivism; for ciclopirox and itraconazole there may be indifference, synergy or additivism.

Tinea capitis in Cleveland: survey of elementary school students

BACKGROUND

Tinea capitis, a fungal infection of the scalp, is of increasing public health importance, and Trichophyton tonsurans has become the primary causative agent in North America.

OBJECTIVES

To determine the prevalence of dermatophyte-positive scalp cultures among elementary schoolchildren in Cleveland, Ohio, describe predisposing factors, and measure the antifungal susceptibility of isolates collected.

OBSERVATIONS

A total of 937 children from 8 Cleveland elementary schools were cultured for the presence of dermatophytes; 122 children (13%), all of whom were African American, had dermatophyte-positive cultures of the scalp. Sixty percent of cases were asymptomatic, indicating a carrier state. Race, scaling, and the use of anti-dandruff shampoo were associated with increased likelihood of infection. T tonsurans was the only organism isolated (except 1 Microsporum canis isolate). All isolates were susceptible to fluconazole, griseofulvin, itraconazole, and terbinafine.

CONCLUSIONS

T tonsurans was the predominant dermatophyte isolated. Further multicenter studies are needed to confirm the predominance of dermatophyte-positive scalp cultures among African American children and to determine modifiable and preventable risk factors.

Clinical Trichophyton rubrum Strain Exhibiting Primary Resistance to Terbinafine

The in vitro antifungal susceptibilities of six clinical Trichophyton rubrum isolates obtained sequentially from a single onychomycosis patient who failed oral terbinafine therapy (250 mg/day for 24 weeks) were determined by broth microdilution and macrodilution methodologies. Strain relatedness was examined by random amplified polymorphic DNA (RAPD) analyses. Data obtained from both broth micro- and macrodilution assays were in agreement and revealed that the six clinical isolates had greatly reduced susceptibilities to terbinafine. The MICs of terbinafine for these strains were >4 μg/ml, whereas they were <0.0002 μg/ml for the susceptible reference strains. Consistent with these findings, the minimum fungicidal concentrations (MFCs) of terbinafine for all six strains were >128 μg/ml, whereas they were 0.0002 μg/ml for the reference strain. The MIC of terbinafine for the baseline strain (cultured at the initial screening visit and before therapy was started) was already 4,000-fold higher than normal, suggesting that this is a case of primary resistance to terbinafine. The results obtained by the broth macrodilution procedure revealed that the terbinafine MICs and MFCs for sequential isolates apparently increased during the course of therapy. RAPD analyses did not reveal any differences between the isolates. The terbinafine-resistant isolates exhibited normal susceptibilities to clinically available antimycotics including itraconazole, fluconazole, and griseofulvin. However, these isolates were fully cross resistant to several other known squalene epoxidase inhibitors, including naftifine, butenafine, tolnaftate, and tolciclate, suggesting a target-specific mechanism of resistance. This is the first confirmed report of terbinafine resistance in dermatophytes.

Clinical Trichophyton rubrum strain exhibiting primary resistance to terbinafine

The in vitro antifungal susceptibilities of six clinical Trichophyton rubrum isolates obtained sequentially from a single onychomycosis patient who failed oral terbinafine therapy (250 mg/day for 24 weeks) were determined by broth microdilution and macrodilution methodologies. Strain relatedness was examined by random amplified polymorphic DNA (RAPD) analyses. Data obtained from both broth micro- and macrodilution assays were in agreement and revealed that the six clinical isolates had greatly reduced susceptibilities to terbinafine. The MICs of terbinafine for these strains were >4 microg/ml, whereas they were <0.0002 microg/ml for the susceptible reference strains. Consistent with these findings, the minimum fungicidal concentrations (MFCs) of terbinafine for all six strains were >128 microg/ml, whereas they were 0.0002 microg/ml for the reference strain. The MIC of terbinafine for the baseline strain (cultured at the initial screening visit and before therapy was started) was already 4,000-fold higher than normal, suggesting that this is a case of primary resistance to terbinafine. The results obtained by the broth macrodilution procedure revealed that the terbinafine MICs and MFCs for sequential isolates apparently increased during the course of therapy. RAPD analyses did not reveal any differences between the isolates. The terbinafine-resistant isolates exhibited normal susceptibilities to clinically available antimycotics including itraconazole, fluconazole, and griseofulvin. However, these isolates were fully cross resistant to several other known squalene epoxidase inhibitors, including naftifine, butenafine, tolnaftate, and tolciclate, suggesting a target-specific mechanism of resistance. This is the first confirmed report of terbinafine resistance in dermatophytes.

Collaborative evaluation of optimal antifungal susceptibility testing conditions for dermatophytes

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 degrees 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 degrees C, an incubation period of 7 days, and MIC-0.

Use of the sensititre colorimetric microdilution panel for antifungal susceptibility testing of dermatophytes

The Sensititre YeastOne antifungal panel was used to test 49 dermatophytes belonging to the species Epidermophyton floccosum, Microsporum gypseum, Microsporum canis, Trichophyton tonsurans, Trichophyton rubrum, and Trichophyton mentagrophytes. The MICs of four antifungals obtained with the Sensititre YeastOne antifungal panel were compared with those obtained by the reference NCCLS microdilution method. The levels of agreement between the two methods (<or=2 dilutions) were 81.6% with amphotericin B, 87.7% with itraconazole, 67.3% with fluconazole, and 69.4% with ketoconazole.

Antimicrobial effect of resveratrol on dermatophytes and bacterial pathogens of the skin

The phytoalexin resveratrol is commonly found in food and drinks, including red wine, grapes, and peanuts. Many studies have shown that this compound has anti-inflammatory properties, and it has been ascribed as having health benefits that help to prevent cancer and coronary heart disease. A treatment that combines antimicrobial and anti-inflammatory actions may be desirable for alleviating many skin conditions that range in severity. Therefore, we evaluated the antimicrobial activity of resveratrol against bacteria and dermatophytes that are major etiologic agents of human skin infections. Using the broth microdilution protocol of the National Committee for Clinical Laboratory Standards (NCCLS) M7-A5, growth of the bacterial species Staphylococcus aureus, Enterococcus faecalis, and Pseudomonas aeruginosa was inhibited at 171-342 microg/mL of resveratrol in the solvent dimethyl sulfoxide. Using the NCCLS protocol M38-P, activity against the fungal species Trichophyton mentagrophytes, Trichophyton tonsurans, Trichophyton rubrum, Epidermophyton floccosum, and Microsporum gypseum was also tested. The growth of dermatophytes was inhibited at 25-50 microg/mL of resveratrol. Thus, this study indicates a novel application for resveratrol, a molecule of plant defense, to combat human fungal pathogens. Resveratrol and its analogs may have wide application to skin conditions that afflict a significant portion of our population, and may also have promising clinical potentials in diabetic wounds.

Candida: a causative agent of an emerging infection

Incidences of infections due to Candida have increased over the last 15-20 y. This increase in the incidence and the high associated mortality rate despite therapy has focused the attention on this disease and prompted investigators to undertake research aimed at understanding the pathogenesis of this disease as well as methods to treat it. This paper discusses recent developments in the Candida field and the impact they have on patient management.

Antifungal susceptibility testing: practical aspects and current challenges

Development of standardized antifungal susceptibility testing methods has been the focus of intensive research for the last 15 years. Reference methods for yeasts (NCCLS M27-A) and molds (M38-P) are now available. The development of these methods provides researchers not only with standardized methods for testing but also with an understanding of the variables that affect interlaboratory reproducibility. With this knowledge, we have now moved into the phase of (i) demonstrating the clinical value (or lack thereof) of standardized methods, (ii) developing modifications to these reference methods that address specific problems, and (iii) developing reliable commercial test kits. Clinically relevant testing is now available for selected fungi and drugs: Candida spp. against fluconazole, itraconazole, flucytosine, and (perhaps) amphotericin B; Cryptococcus neoformans against (perhaps) fluconazole and amphotericin B; and Aspergillus spp. against (perhaps) itraconazole. Expanding the range of useful testing procedures is the current focus of research in this area.

In vitro activities of 10 antifungal drugs against 508 dermatophyte strains

We have tested 508 strains belonging to 24 species of dermatophytes against 10 antifungal drugs following mainly the NCCLS (M38-P) standard for filamentous fungi. However, several important factors, such as the temperature (28 versus 35 degrees C) and time of incubation (4 to 10 days versus 21 to 74 h), have been modified. The antifungals used were itraconazole, ketoconazole, miconazole, clotrimazole, voriconazole, terbinafine, amphotericin B, fluconazole, UR-9825, and G-1. In general, with the exception of fluconazole and G-1, all antifungals were shown to be highly effective.

A large-scale North American study of fungal isolates from nails: the frequency of onychomycosis, fungal distribution, and antifungal susceptibility patterns

BACKGROUND

Onychomycosis, a fungal infection of the nail bed, is responsible for up to 50% of nail disorders. Although several surveys have been conducted in different parts of the world, there have been no multicenter epidemiologic surveys of onychomycosis in North America.

OBJECTIVE

A 12-center study was undertaken to (1) determine the frequency of onychomycosis, (2) identify organisms recovered from the nails, and (3) determine the antifungal susceptibility of isolates.

METHODS

A total of 1832 subjects participated in this study and completed a comprehensive questionnaire, and nail clippings were collected for potassium hydroxide examination and culturing.

RESULTS

The frequency of onychomycosis, as defined by the presence of septate hyphae on direct microscopy and/or the recovery of a dermatophyte, was found to be 13.8%. In general, the dermatophyte isolates were susceptible to the antifungals tested.

CONCLUSION

Because of the limited number of large-scale studies, the baseline incidence is not firmly established. However, the higher frequency of onychomycosis in this study may confirm the suspected increase in incidence of disease in North America.