Variability in ultrastructure of Clostridium botulinum spores

Abstract

The ultrastructure of spores of Clostridium botulinum strains 78A, 17B (nonproteolytic), and C51C3 was investigated. Electron photomicrographs revealed the following: strain 78A: the oval spores, enveloped by multilayered exosporia, were normally found within swollen sporangia. The spore coat contained a distinct outer layer and a thicker inner coat. Strain 17B: the oval spores were covered by open-ended, sheath-like exosporia. Some spores were enclosed within slightly swollen sporangia, while most were present as free spores. A layered, electron-translucent outer coat and an electron-dense inner coat comprised the spore coat. Strain C51C3: the oval to cylindrical spores were seldom found within intact sporangia. The spore coat was a single, thin, electron-dense layer. Exosporial layers were in apposition to the spore coat.