An ultrastructural study of pale eumycetoma grains.

The electron microscopic appearances of grains from seven patients with pale grain eumycetoma infections have been studied. The infecting fungi were Pseudallescheria boydii (2), Fusarium sp. (1), Acremonium kiliense (1), a non-sporing mould (2) and Trichophyton violaceum (1). P. boydii grown in vitro and grains from a Madurella mycetomatis infection were used for comparison. The most important ultrastructural features of the pale eumycetoma grains were the gross thickening of the fungal cell walls maximal at the periphery of the grain, the predominance of grossly disorganised hyphae and the appearance of cytoplasmic membrane systems. In some areas adjacent cell walls appeared to fuse. These changes may account for some of the well recognised difficulties in isolating organisms from eumycetoma grains and treating the infections with antifungal drugs.