Direct Detection Methods of the Dermatophytes
المؤلف:
Patricia M. Tille, PhD, MLS(ASCP)
المصدر:
Bailey & Scotts Diagnostic Microbiology
الجزء والصفحة:
13th Edition , p734-735
2025-11-27
44
Stains. Calcofluor white or potassium hydroxide preparations reveal the presence of hyaline septate hyphae and/or arthroconidia (see Figures 1 and 2). Direct microscopic examination of infected hairs may reveal the hair shaft to be filled with masses of large arthroconidia (4 to 7 µm) in chains, characteristic of an endothrix type of invasion. In other instances, the hair shows external masses of spores that ensheath the hair shaft; this is characteristic of the ectothrix type of hair invasion. Hairs infected with Trichophyton schoenleinii reveal hyphae and air spaces within the shaft.
Fig1. Fungi commonly seen in clinical specimens. A, This potassium hydroxide preparation of a skin scraping from a patient with a dermatophyte infection shows septate hyphae intertwined among epithelial cells. (Phase-contrast microscopy; ×500.) B, This calcofluor white stain of urine demonstrates Candida albicans. C, The deeply staining, small, uniform yeast cells in this histologic section of lung tissue are typical of Histoplasma capsulatum. (Methenamine silver stain; ×430.)
Fig2. Calcofluor white stain of sputum showing intracellular yeast cells of H. capsulatum (arrows). The cells are 2 to 5 µm in diameter.
Antigen-Protein. Antigen-protein—based assays are not useful for the detection or identification of dermatophytes.
Nucleic Acid Amplification. Nucleic acid amplification assays for dermatophytes are not routine; these are available in research settings.
Cultivation. Because the dermatophytes generally present a similar microscopic appearance in infected hair, skin, or nails, final identification typically is made by culture. A summary of the colonial and microscopic morphologic features of these fungi is presented in Table 1. Figure 3 presents an identification schema useful to the clinical laboratory for identification of commonly encountered dermatophytes. The schema begins with the microscopic features of the dermatophytes that may be visible in the initial examination of the culture. In many instances, the primary recovery medium fails to function as well as a sporulation medium. Often the initial growth must be subcultured onto cornmeal agar or potato dextrose agar to induce sporulation.
Table1. Characteristics of Dermatophytes Commonly Recovered in the Clinical Laboratory
Fig3. Dermatophyte identification schema. (From Koneman EW, Roberts GD: Practical laboratory mycology, ed 3, Baltimore, 1985, Williams & Wilkins.)
الاكثر قراءة في الفطريات
اخر الاخبار
اخبار العتبة العباسية المقدسة
