Laboratory Diagnosis of Medically Important Dermatophytes: Traditional Methods and New Developments
Authors: Yapalak Zehra Leyla , Atılan Kübra 
Published: August 2023

Accurate and rapid identification of the causative agent in dermatophyte infections plays a key role in patient management and planning of appropriate treatments. Direct examination, Wood's lamp, microscopy, culture, polymerase chain reaction (PCR), post-PCR identification methods, matrix-assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF MS) and genetic analyzes are the basic diagnostic approaches used in the diagnosis of dermatophytes. Each of these methods has certain advantages and disadvantages, and studies on new targets are continuing to increase the sensitivity of clinical diagnosis. Although direct examination of dermatophyte lesions (dermoscopic findings) provides non-invasive and rapid results, the inadequacy of identifying the causative agent is the most important disadvantage of this approach. While the Wood's lamp is similarly a non-invasive, low-cost, and fast diagnostic method, it is a significant disadvantage that not all dermatophyte species fluoresce. In microscopic evaluations, dermatophytes can be identified by examining species and genus specific (unique) characteristics, but this approach requires experienced personnel and special equipment. Low cost and quick results are the advantages of microscopy, while its inability to distinguish between dead and live fungi is its most important limitation. Culture methods are low-cost, easy-to-apply and other diagnostic methods that can distinguish between species, and have certain disadvantages such as specialized identification procedures, possibility of contamination with saprophytic fungi, and results in days to weeks. Nucleic acid-based molecular methods are widely used in the clinical microbiology laboratory for the rapid and specific identification of fungi, as well as for the detection of the etiologic agent directly from the clinical sample. PCR has become the most preferred molecular method with its high sensitivity and ability to distinguish between species, also advanced diagnostic protocols based on PCR-ELISA (Enzyme Linked Immunosorbent Assay) and PCR-RFLP (Restriction Fragment Length Polymorphism) after conventional PCR have been defined. Different modifications of the PCR method such as real-time PCR, nested-PCR, multiplex PCR have been defined in the diagnosis of dermatophytosis, with these protocols, sensitivity has been increased, contamination risk has been reduced, and simultaneous identification of multiple pathogens has been possible. The inability of molecular-based methods such as PCR-based tests, which can give results in a short time, and sequence analysis of specific gene regions, which is the gold standard approach for species-level identification, to distinguish dead and living fungi, is an important disadvantage for clinical evaluations. Although investigating antibodies against fungal structures with ELISA, another rapid diagnostic method, is a highly specific approach, false positive results associated with previous infections reduce the clinical sensitivity of the method. MALDI-TOF MS, which is increasingly used, is a new identification method developed as an alternative to traditional and molecular methods, and has advantages such as high sensitivity, results in minutes and hours, and low workload requirement. The MALDI-TOF MS method can distinguish between dermatophyte species at the genus and species level, but problems with the size and scope of the reference library are the most important limiting factors for the descriptive power of the method. While evaluations of the specific advantages and disadvantages of each of the various diagnostic methods used in the diagnosis of dermatophytes take place on a wide scale, it is important for clinical laboratories to decide which method is most appropriate in their own regional conditions.