Are giant cells conidia in Sporothrix schenckii? -Freeze-fracture electron microscopic observation-.

Abstract

Sporothrix schenckii is a well-known pathogenic dimorphic fungus. In this study, we focused on the plasma membrane ultrastructures of giant cells of S. schenckii seen mainly on Sabouraud's dextroseagar slant medium. In the organisms grown for 1, 2, 3, 4, 6 and 8 weeks at 27 and 37 degrees C on brain heart infusion and Sabouraud's dextrose agar slant media, the number of conidia, hyphae, brownish and non-brownish giant cells were counted in ten separated areas under light microscope (x100) to determine the culture conditions under which giant cells were generated. The results showed that brownish giant cells were predominantly seen after longer cultivation periods. Using freeze-fracture electron microscopy, larger oval- or round shaped cells can be identified as conidia by their plasma membrane ultrastructure characteristics, i.e, trench-like invaginations seen in ordinary mature conidia (Maeda M et al.; Can J Microbiol 33: 40, 1987). From these structural features seen by freeze-fracture electron microscopy, giant cells appeared possibly be conidia and were suggested to be starved because of their predominant existence under longer cultivation conditions.