Conventional and molecular diagnostics for detection of causative fungi in clinical samples of human dermatomycosis

Abstract

Background Dermatomycosis affects millions of people worldwide; the availability of data on the prevalence of superficial fungal infections and some associated epidemiological factors in our region is little. Objective To compare conventional and molecular methods to characterize some fungal species causing human mycotic infection. Patients and methods The present cross-sectional study of fungal skin diseases was done on 100 patients. Skin scrapings and nail cuttings were subjected to direct microscopic examination using potassium hydroxide and lactophenol cotton blue, followed by culturing on Sabouraud’ dextrose agar. HiCrome agar was used for characterization of Candida species. Molecular diagnosis of some fungal isolates was performed by sequencing the ribosomal DNA internal transcribed spacer region. Results Tinea capitis was the commonest clinical presentation in 48% of cases, followed by tinea corporis 20% and tinea faciei 13%. Fungi were demonstrated in 88% of cases by direct microscopy and/or culture. Direct microscopy was positive in 51% of cases. A higher percentage of positivity 77% was obtained from samples cultured on Sabouraud’ dextrose agar. Dermatophytes were isolated from patients who complained of tinea capitis and tinea corporis (75 and 70%, respectively). Comparing molecular with conventional results, it was found that molecular identification was confirmatory to conventional results, except in two isolates: Chrysosporium lobatum was previously diagnosed as Chrysosporium tropicum and Trichophyton interdigitale was previously diagnosed as Trichophyton mentagrophytes by conventional methods. Conclusion Trichophyton violaceum and Microsporum canis were the main etiologic agents of tinea capitis (45.8 and 27%, respectively). Epidermophyton floccosum was only isolated from four cases of tinea corporis and one of the tinea cruris. Candida species were the main causal agents of onychomycosis. Acremonium spinosum and C. lobatum appeared in this study as new etiologic agents of nail infections. Molecular identification is confirmatory to conventional results, but it is expensive and faces some difficulties, in our country, its use is encouraged to identify dermatophytes in atypical isolates.

Keywords

• candidiasis
• onychomycosis
• rdna sequencing
• superficial mycoses