Ultrastructure of the Trichophyton mentagrophytes Septum

A septum-rich fraction was prepared from Triehophyton mentagrophytes, and the ultrastructural investigation of septa was carried out by shadowing and thin section electron microscopy before and after enzymatic and/or alkaline treatments. Tri-lamellar structure, consisting of an electron lucid middle layer and two outer electron dense layers, was observed by thin section electron microscopy. By shadowing electron microscopy, the surface ultrastructure of septa exhibited a randomly orientated microfibrillar network structure, which may correspond to the electron dense outer layers of the septum observed in thin section preparations. However, shadowed septa after papain digestion revealed a spiral arrangement of microfibrils consisting of rodlet-like units, which disappeared during chitinase treatment. This spiral structure may therefore be composed primarily of chitin. It was suggested that this spirally arranged microfibrils may correspond to the electron lucid middle layer observed in thin section preparations.