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Dermatophytes fungi in clinical specimens: Microscopic exam; Culture; Species identification; Molecular diagnosis (PCR).

 

Information 01/12/15.

 

The conventional etiological diagnosis of dermatophytosis is usually accomplished using microscopic examination of samples treated with KOH, or by culturing samples, with subsequent identification of the species microscóipica dermatophyte. Microscopic examination can give false positive and false negative results and in some samples from lesions as onychomycosis, can not differentiate between dermatophyte and non-dermatophyte infections. The final diagnosis depends on conventional culture isolation, but this method is very sensitive in onychomycosis cases and provides late results.

The molecular methods such as PCR are fast, sensitive and specific. We used several PCR methods aimed at detecting the gene of chitin synthetase I (CHS1) dermatophytes, which have been applied to identify fungal isolates in culture or to detect their presence in flakes skin scrapings. In addition, a method has been evaluated nested PCR (nested) able to detect any of the three genera (Trichophyton, Microsporum and Epidermophyton). These authors, comparative study samples of onychomycosis by microscopy, culture, PCR simple and nested PCR (nested) have obtained the diagnosis in 63%, 25%, 51% and 79% of cases, respectively by the four methods compared, so it is advisable to use the method of nested PCR (nested) for the diagnosis of onychomycosis.

The interest in applying nested PCR (nested) to onychomycosis, is that although most fungal onychomycosis are produced by dermatophytes, can also be produced by yeast or other filamentous fungi not dermatophytes. Differentiating these etiology is of interest because they differ in their therapeutic response, as antifungal treatments do not possess the same activity against various fungi of onychomycosis producers. For example, griseofulvin is only effective against dermatophytes and lacks activitie against Candida spp., Or other filamentous fungi not dermatophytes. Terbinafine possesses activity against dermatophytes but has only fungistatic activity against Candida albicans.

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