الفهرس 
The DermatophytesOnly 14 pages are availabe for public view
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Abstract
ermatophyte infection constitutes one of the most important groups of fungal infections in the world. Dermatophytes have three genera, Trichophyton, Microsporum, and Epidermophyton. Invasion of the keratinized tissues causes infections in skin, nails or hairs. T.rubrum, T.violecium, T. menagrophytes, T. tonsurans, E. floccosum and M canis are examples of dermatophytes that are isolated as etiologic agents from patients having tinea.
It is sometimes difficult to rely completely on results of direct microscopic examination with KOH to establish the diagnosis of different fungal skin infection as it lacks sufficient sensitivity; however it’s highly efficient as a screening technique. Culture on the specific media of dermatophytes will ensure the diagnosis reaching to the species level and sometimes to strain level, however it may be time consuming, costly, different culture media are needed for proper identification, in addition to the presence of special skills and experiences as the morphological character of some species are atypical, however, the culture still remains the standard procedure.
As clinical presentation is often atypical these dermatophytes are identified to species level by morphological features using conventional morphological techniques such as macroscopic examination of large, mature colonies and different culture techniques. Further identification characteristics include nutritional requirements (such as vitamin and amino acid utilization), urease production, in vitro hair perforation, Bromocresol purple-milk solids-glucose medium, etc.
Because of the long time required for identification and the lack of significant morphological features, the identification of dermatophyte species by conventional method has been impeded. Thus newer fungal diagnostic methods are needed as identification of the etiological agent is required not only for accurate diagnosis, but also for post-therapeutic strategies.
Phenotypic variability within isolates of some dermatophytes like T. rubrum has been demonstrated in terms of gross morphology. The formation of red color on the colony is an important character for the identification of this fungus. Color variation may be induced by alternation in culture media, pH and culture temperature.
Sometimes the appearance of colonies of T.rubrum resembles that of T. mentagrophytes, if it can not form the red color. Furthermore some T.rubrum strains are positive in the hair perforation test and urease test.
So, the great diversity of profiles between the T. mentagrophytes group and T. rubrum seems particularly interesting and makes the two species quite in distinguishable, with the classical technique as their identification is often difficult.
Since the distinguishing morphological characteristics of a fungus are frequently too limited to allow its identification physiological and biochemical techniques are applied, as has been routinely done for the yeasts however, for poorly differentiated filamentous fungi, these methods are laborious, time consuming and somewhat variable and provide insufficient taxonomic resolution
Clinical research in the dermatophytes has traditionally focused on descriptions of the pathogens, the disease, and the epidemiology. There has been some work with molecular studies that have focused on attention on these significant pathogens and allowed researchers to move quickly to the development of new diagnostic techniques and therapies. Genomic sequences allowed for the development of more accurate and sensitive diagnostics for dermatophyte infections.
In addition genome sequences generated through this effort allowed researchers to identify repetitive sequences that are common to all dermatophyte, or that are unique to specific species or strains. These repetitive sequences could be used to fingerprint strains and monitor infections.
The aim of molecular studies in biodiversity is fourfold: (i) phylogenetic studies, i.e., tracing back the most probable course of evolution and the historic coherence between groups at higher taxonomic ranks; (ii) taxonomic studies, mostly at the level of genera and species; (iii) diagnostic applications, i.e., recognition of defined taxonomic entities; and (iv) epidemiology and population genetics, i.e., monitoring outbreaks of sub specific entities with respect to the analysis of populations and their mode of reproduction
Using molecular biological methods for differentiation between the genotypic characteristics of the species of dermatophytes are more specific, precise, rapid, and are less likely to be affected by external influences such as temperature variations and chemotherapy.
These molecular methods, include the analysis of restriction fragment length polymorphisms (RFLP), amplified fragment length polymorphism (AFLP), comparisons of sequences of the internal transcribed spacer 1 (ITS1) regionو random amplification of polymorphic DNA (RAPD), arbitrarily primed PCR (AP-PCR), and PCR fingerprinting, nested PCR, all of which have brought important progress in distinguishing between species and strains.
However, most of these techniques are complex, laborious, time-consuming, and not easily employable for routine identification of dermatophytes. It worth mentioning that PCR-RAPD technology is a technique of simple execution, rapid in comparison to other techniques of molecular biology and it can be applied in cases where it is necessary to identify strains not presenting typical morphological characteristic and in the absence of specific nucleotide sequence information for the many dermatophyte species.
Although AP-PCR in contrast to others is simple, rapid and practical for identification of dermatophyte isolates to the species and strain level within one day that is independent of the culture variations.
PCR is a technique of simple execution, rapid and can be applied in cases where it’s necessary to identify strains not presenting typical morphological characteristic, therefore this method can be of great utility instead of culture as it would allow rapid diagnosis of the species leading to a better management of infections caused by these fungi.
A disadvantage of the use of PCR fingerprinting for identifying dermatophytes is the relatively higher cost in comparison to the classical method.
The techniques utilized for identification of various types of dermatophytes were as follow:
AP-PCR, ITS regions and RAPD were used for identification of T.rubrum. The ITS region are considered the most informative technique used for identification of T. violecium and T. canis. While RLFP analysis, RAPD and ITS regions were used for identification of T. mentagrophyte.
The future success of sequencing-based approaches will depend on the choice of DNA target, the reliability of the result, and the availability of a validated sequence database for query and comparisons. Future studies will be required to determine sequence homology breakpoints and to asses the accuracy of molecular-based species identification in various groups of medically important filamentous fungi.
At this time, a polyphasic approach to identification that combines morphologic and molecular methods will ensure the greatest success in the management of patients with fungal infections.