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

Antifungal Patterns of Dermatophytes: A Pathway to Antifungal Stewardship in Eastern India

Background Dermatophytosis is a superficial fungal infection caused by a group of pathogenic keratinophilic fungi. The increase in the incidence of superficial fungal infections, combined with the emergence of antifungal resistance, represents both a global health challenge and a considerable economic burden. Recent years have witnessed a surge in dermatophytosis cases, accompanied by the emergence of antifungal-resistant strains. This study aimed to analyze the in vitro antifungal susceptibility patterns and determine the minimum inhibitory concentrations (MIC) of antifungal drugs among isolated species using the broth microdilution method. Methodology This cross-sectional study was conducted between September 2021 and August 2022. Patients with symptoms or clinical features of fungal infection, including skin, hair, and nail lesions indicative of Tinea infections, were included. Samples underwent processing, including potassium hydroxide (KOH) mounting, direct microscopic examination, and culture on Sabouraud Dextrose Agar (SDA) with antibiotics. Antifungal susceptibility testing was subsequently conducted. Results Trichophyton mentagrophytes emerged as the most common isolate among patients with Tinea infections. MIC values of various drugs were analyzed, with itraconazole exhibiting a minimum MIC of 0.03 µg/ml and a maximum of 0.50 µg/ml. Terbinafine showed an MIC of 0.010 µg/ml and a maximum of 1.00 µg/ml. Ketoconazole had a minimum MIC of 0.03 µg/ml and a maximum of 0.50 µg/ml. Fluconazole exhibited a minimum MIC of 0.10 µg/ml and a maximum of 1.00 µg/ml. Lastly, miconazole demonstrated a minimum MIC of 0.03 µg/ml and a maximum of 2.00 µg/ml. Conclusion Accurate diagnosis is crucial for fungal infections to enable early treatment and reduce transmission. With an increasing trend in resistance among dermatophytes, there is a growing need to conduct susceptibility testing of antifungal agents, particularly in cases of long-term infections, recurrent infections, and individuals who do not respond to medication.

In vitro activities of antifungal drugs against a large collection of Trichophyton tonsurans isolated from wrestlers

BACKGROUND

Trichophyton tonsurans is the most common agent causing tinea gladiatorum in wrestlers, and limited data on susceptibility profiles of Trichophyton tonsurans are available.

OBJECTIVES

We aimed to assess the in vitro activity of the common antifungal drug against a large collection of T tonsurans.

MATERIALS/METHODS

The in vitro activities to eight common antifungal drugs (sertaconazole, itraconazole, clotrimazole, fluconazole, butenafine, tolnaftate, terbinafine and griseofulvin) against 128 clinical isolates of T tonsurans strains, obtained from wrestlers with dermatophytosis, were performed according to CLSI M38-A2 broth microdilution document.

RESULTS

The geometric mean minimum inhibitory concentration was the lowest for tolnaftate (0.022 µg/mL), followed by itraconazole (0.026 µg/mL), terbinafine (0.033 µg/mL), butenafine (0.088 µg/mL), griseofulvin (0.566 µg/mL), sertaconazole (2.875 µg/mL), clotrimazole (3.419 µg/mL) and fluconazole (12.540 µg/mL).

CONCLUSIONS

Evaluation of antifungal susceptibility of dermatophytes showed that tolnaftate and itraconazole were the most effective drugs against T tonsurans and fluconazole had the least effect.

Determination of antifungal minimum inhibitory concentration and its clinical correlation among treatment failure cases of dermatophytosis

Introduction:

Dermatophytes are most common infectious agents causing superficial mycosis worldwide. A number of topical as well as systemic antifungal drugs are available for treatment of dermatophytosis. Superficial mycosis caused by dermatophytes can be easily treated by topical or oral antifungal drugs, but in the course of time, an increased number of treatment failure cases are appearing. Possible cause for treatment failure could be poor patient compliance, poor drug penetration into affected lesion, and also drug resistance in dermatophytes. The aim of this study is to investigate minimum inhibitory concentration and clinical correlation in treatment failure cases of dermatophytosis.

Methods:

Skin, hair and nail samples were collected from treatment failure cases of dermatophytosis. A total 75 isolates were tested for MIC against four antifungal drugs in the study. Fluconazole, itraconazole, ketoconazole and terbinafine were the antifungal drugs tested using broth microdilution method. MIC₅₀ and MIC₉₀ values were recorded.

Results:

A total of 75 dermatophytic isolates were tested. Dermatophytic isolates in this study were Trichophyton mentagrophytes (n = 31), T. rubrum (n = 13), T. tonsurans (n = 12), T. verrucosum (n = 9), M. gypseum (n = 5), E. floccosum (n = 4) and T. violaceum (n = 1). MIC₉₀ value for fluconazole and terbinafine was significantly higher.

Conclusion:

MIC of 17.33% isolates for fluconazole and 33.33% isolates for terbinafine were lower than cut-off value, which indicates that not all treatment failure cases are due to drug resistance.

Determination of minimum inhibitory concentrations of itraconazole, terbinafine and ketoconazole against dermatophyte species by broth microdilution method

PURPOSE

Various antifungal agents both topical and systemic have been introduced into clinical practice for effectively treating dermatophytic conditions. Dermatophytosis is the infection of keratinised tissues caused by fungal species of genera Trichophyton, Epidermophyton and Microsporum, commonly known as dermatophytes affecting 20-25% of the world's population. The present study aims at determining the susceptibility patterns of dermatophyte species recovered from superficial mycoses of human patients in Himachal Pradesh to antifungal agents; itraconazole, terbinafine and ketoconazole. The study also aims at determining the minimum inhibitory concentrations (MICs) of these agents following the recommended protocol of Clinical and Laboratory Standards Institute (CLSI) (M38-A2).

METHODOLOGY

A total of 53 isolates of dermatophytes (T. mentagrophyte-34 in no., T. rubrum-18 and M. gypseum-1) recovered from the superficial mycoses were examined. Broth microdilution method M38-A2 approved protocol of CLSI (2008) for filamentous fungi was followed for determining the susceptibility of dermatophyte species.

RESULTS

T. mentagrophyte isolates were found more susceptible to both itraconazole and ketoconazole as compared to terbinafine (MIC50: 0.125 µg/ml for itraconazole, 0.0625 µg/ml for ketoconazole and 0.5 µg/ml for terbinafine). Three isolates of T. mentagrophytes (VBS-5, VBSo-3 and VBSo-73) and one isolate of T. rubrum (VBPo-9) had higher MIC values of itraconazole (1 µg/ml). Similarly, the higher MIC values of ketoconazole were observed in case of only three isolates of T. mentagrophyte (VBSo-30 = 2 µg/ml; VBSo-44, VBM-2 = 1 µg/ml). The comparative analysis of the three antifungal drugs based on t-test revealed that 'itraconazole and terbinafine' and 'terbinafine and ketoconazole' were found independent based on the P < 0.005 in case of T. mentagrophyte isolates. In case of T. rubrum, the similarity existed between MIC values of 'itraconazole and ketoconazole' and 'terbinafine and ketoconazole'.

CONCLUSION

The MIC values observed in the present study based on standard protocol M38-A2 of CLSI 2008 might serve as reference for further studies covering large number of isolates from different geographic regions of the state. Such studies might reflect on the acquisition of drug resistance among isolates of dermatophyte species based on MIC values.

Isolation, Identification, and In Vitro Antifungal Susceptibility Testing of Dermatophytes from Clinical Samples at Sohag University Hospital in Egypt

Aim

The objective of this study was to isolate, identify, and explore the in-vitro antifungal susceptibility pattern of dermatophytes isolated from clinically suspected cases of dermatophytosis (tinea infections) attending the Dermatology Outpatient Clinic.

Methods

This study was conducted at Sohag University Hospital from December 2014 to December 2015. Clinical samples (e.g., skin scrapings and hair stumps) were collected under aseptic precautions. The identification of dermatophytes was performed through microscopic examination using 10% potassium hydroxide (KOH) with 40% dimethyl sulphoxide (DMSO) mounts and culture on Sabouraud dextrose agar (SDA) and on Dermasel agar base media, both supplemented with chloramphenicol and cycloheximide. All dermatophytes isolates were subjected to antifungal susceptibility testing using the agar-based disk diffusion (ABDD) method against Clotrimazole, Miconazole, Fluconazole, and Griseofulvin. Data were analyzed via SPSS 16, using Chi square and a screening test (cross-tabulation method).

Results

A total of 110 patients of dermatophytosis were studied. The patients were clinically diagnosed and mycologically confirmed as having tinea capitis (49), tinea corporis (30), tinea pedis (16), tinea cruris (9), or tinea barbae (6). The dermatophytes isolates belonged to 4 species: Microsporum canis 58 (52.7%), Microsporum gypseum 23 (20.9%), Trichophyton mentagrophytes 18 (16.4%), and Microsporum audouinii 11 (10%). The most effective antifungal drugs tested were Clotrimazole, followed by Miconazole (95.5% and 84.5% of isolates were susceptible, respectively).

Conclusion

Every patient with a tinea infection should be properly studied for a mycological examination and should be treated accordingly. Dermasel agar is more useful as an identification medium in the isolation of dermatophytes. The ABDD method appears to be a simple, cost-effective, and promising method for the evaluation of antifungal susceptibility of dermatophytes.

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.

Onychomycosis: clinical, mycological and in vitro susceptibility testing of isolates of Trichophyton rubrum

BACKGROUND

Onychomycosis or nail fungal infection is the most common nail disease. Despite the wide range of studies on this condition, it remains difficult to establish the correct diagnosis and effective treatment.

OBJECTIVES

To evaluate the efficacy of classical laboratory methods for the diagnosis of onychomycosis, and the in vitro susceptibility of the its main etiological agent to antifungals used in routine.

METHODS

Nail samples of 100 patients with clinically suspected feet onychomycosis were collected to confirm the diagnosis by direct mycological examination and fungal culture. In vitro antifungal susceptibility testing was performed against strains of the main dermatophyte isolated by microdilution, according to the standardized protocol (M38-A2 - CLSI)

RESULTS

Clinical diagnosis of onychomycosis was confirmed by laboratory analysis in 59% of patients. Of these, 54.2% were positive only in direct mycological examination, 44.1% in direct mycological examination and culture, and one case (1.7%) was positive only in culture, resulting in weak agreement between these tests (Kappa = 0.385; p <0.001) High minimum inhibitory concentration values of fluconazole and itraconazole were observed in 66.7% and 25.0% of isolates of T. rubrum tested. Additionally, high MIC values of terbinafine and ciclopirox was detected in only one isolate, and this was one of the strains in which in vitro activity of itraconazole and fluconazole has not been proven.

CONCLUSIONS

Poor agreement was observed between direct mycological examination and culture for the diagnosis of onychomycosis, with direct mycological examination being significantly more sensitive. Except for fluconazole, the other three antifungals tested showed good in vitro activity against clinical isolates of T. rubrum.

In vitro activities of antifungal drugs against dermatophytes isolated in Tokat, Turkey

BACKGROUND

In this study, we aimed to establish the in vitro antifungal susceptibilities of terbinafine, miconazole, itraconazole, ketoconazole, griseofulvin, and amphotericin B against dermatophyte isolates.

METHODS

One hundred and seventy-seven clinical isolates were tested: Trichophyton rubrum (n = 78), Trichophyton mentagrophytes (n = 49), Epidermophyton floccosum (n = 30), Trichophyton verrucosum (n = 16), and Trichophyton tonsurans (n = 4). The broth microdilution assay for antifungal susceptibility testing of dermatophytes was performed according to Clinical and Laboratory Standards Institute guidelines in the M38-A2 document.

RESULTS

Our minimum inhibitory concentration (MIC) results showed that the values for terbinafine for all dermatophyte isolates were significantly lower than the values for amphotericin B, miconazole, itraconazole, ketoconazole, and griseofulvin. For T. rubrum isolates, amphotericin B was more active than miconazole, itraconazole, and ketoconazole. Among the antifungal drugs tested, griseofulvin had the highest minimum inhibitory concentration values for T. mentagrophytes isolates.

CONCLUSION

Terbinafine was found to be the most effective antifungal drug against all tested dermatophyte isolates. Griseofulvin was the less active antifungal drug against T. mentagrophytes isolates. Performing antifungal susceptibility testing is especially important for screening the development of antifungal resistance.

Histopathology of experimental myiasis in mice as a result of infestation and experimental implantation of Dermatobia hominis larvae

A laboratory model of myiasis as a result of Dermatobia hominis (L.) larvae was developed using mice as hosts. Mice in three groups were each infested with one newly hatched larva and skin biopsies processed for histopathology at 4, 12, and 20 d postinfestation (dpi). Mice in three other groups were each subjected to implantation of one larva collected from an infested (donor) mouse at 4, 12, and 20 dpi. Skin lesions of these receptor mice were then assessed at 10, 14, and 6 d postimplantation (dpimp), respectively. The inflammatory process in infested mice at 4 dpi was discrete, consisting of a thin necrotic layer around the larva, edema, many neutrophils, few eosinophils, mast cells, and proliferation of fibroblasts. At 12 dpi, there was a thicker necrotic layer, edema, many neutrophils and eosinophils, few mast cells, neoformation of capillaries, proliferation of the endothelium and fibroblasts, and early stages of fibrosis. These histopathological characteristics together with fibrosis were observed over a large area of the lesion at 20 dpi. Mice submitted to larval implantations demonstrated similar skin histopathology to that seen in the infested rodents, 10 dpimp corresponding to 12 dpi and 6 or 14 dpimp to 20 dpi. In all mice, the progressive acute inflammatory process followed a sequence linked to factors such as size of larvae and presence of secretory-excretory products. Both infested mice and those implanted experimentally with D. hominis larvae were shown to be suitable models for the study of the parasite-host relationship in this important zoonotic myiasis.