Direct Microscopic Examination of Fungi
المؤلف:
Patricia M. Tille, PhD, MLS(ASCP)
المصدر:
Bailey & Scotts Diagnostic Microbiology
الجزء والصفحة:
13th Edition , p717
2025-11-15
57
Direct microscopic examination of clinical specimens has been used for many years; however, its usefulness should be reemphasized. Because the mission of a clinical microbiology laboratory is to provide a rapid and accurate diagnosis, the mycology laboratory can provide this service in many instances by direct examination (particularly the Gram stain) of the clinical specimen submit ted for culture. Microbiologists are encouraged to become familiar with the diagnostic features of fungi commonly encountered in clinical specimens and to recognize them when stained by various dyes. This important procedure often can provide the first microbiologic proof of the etiology of disease in patients with fungal infection. This is the most rapid method currently available.
Tables 1 and 2 present the methods available for direct microscopic detection of fungi in clinical specimens and a summary of the characteristic microscopic features of each. Figure 1 presents photomicrographs of some of the fungi commonly seen in clinical specimens.
Table1. Summary of Methods Available for Direct Microscopic Detection of Fungi in Clinical Specimens
Table2. Summary of Characteristic Features of Fungi Seen in Direct Examination of Clinical Specimens
Table2. Summary of Characteristic Features of Fungi Seen in Direct Examination of Clinical Specimens—cont’d
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.)
Traditionally, the potassium hydroxide preparation has been the recommended method for direct microscopic examination of specimens. However, the calcofluor white stain now is believed to be superior (see Procedure 1 on the Evolve site). Slides prepared by this method may be observed using fluorescent or bright field microscopy, as is used for the potassium hydroxide preparation; the former is optimal, because fungal cells fluoresce.
PROCEDURE 1
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