Zygomycosis: conventional laboratory diagnosis.

A definitive diagnosis of zygomycosis caused by Mucorales can be made by histopathological examination with or without isolation of the fungus from the same site. Histopathological examination of the tissues affected typically shows characteristic broad, hyaline, ribbon-like, irregular fungal hyphae with wide-angle branching, accompanied by tissue necrosis and angioinvasion of the fungi. Tissue invasion by the fungal hyphae as seen by microscopy is essential to establish the diagnosis. Fungal elements can be stained with Gomori methenamine-silver, periodic acid-Schiff or Calcoflour white stain. All Mucorales grow rapidly on most fungal media such as Sabouraud dextrose agar incubated at 25-30 degrees C. Mucorales from a sterile site or repeated positive cultures of the fungi from a non-sterile site are considered significant in a high-risk patient with predisposing factors for acquisition of zygomycosis. Positive cultures from non-sterile specimens should be interpreted with caution and will require correlation between the finding and the clinical situation.