Fungi

General:

Clinical: Most infections are following exposure to one of numerous natural ubiquitous saprophytes. Of more than 100,000 ubiquitous species, only about 150 are known to cause disease. Except for dermatophytes, tinea versicolor, and candida they are not considered contagious. Serology is generally unreliable, often with a high false negative rate. Fastest and most reliable is considered histopathologic examination, however this identification is usually only to the genus level.

• Normal: Actinomyces, candida cause no clinical problems in small quantities.
• Abnormal:

Resistance:

Morphology: Possibly visible on H & E, where hyaline (colorless) or dematiaceous (naturally pigmented) determinations can be made, but usually requires special stains such as GMS, considered the most ideal, or PAS. GMS can be counterstained with H & E to better evaluate tissue reactivity. The cytoplasm of some fungi, particularly yeast forms of Histoplasma capsulatum variant capsulatum and Blastomyces dermatitidis, are acid fast on AFB staining and potentially can cause confusion. Some fungi autofluoresce under UV light, and others fluoresce when stained with a whitening agent such as calcofluor white (these are all nonspecific, but useful in visualizing sparse or otherwise poorly staining fungal elements); has been used in intraoperative frozen section evaluation, although no better than rapid GMS procedures. Modified Gram stains are also used, such as Brown and Brenn and Brown-Hopps, particularly for actinomyces or nocardia.

Growth characteristics:

Common/important pathogens: