Ultrastructure of Mycoplasma hominis

Abstract

Both thin-sectioning and negative staining were used in an electron microscopic study of the morphology of pleuropneumonia-like organism (PPLO) strain HEp-2 (M. hominis, type-I) grown in an artificial liquid medium. The morphology is quite variable and seems to depend, in part, on the age of the culture. The smallest form observed ("elementary body") is 80 to 100 m[mu]. in diameter. The internal components of the larger PPLO cells (0.5 to 1 [mu]) are variable[long dash]some have ribosomelike granules and nuclear areas of netlike strands, and others have only irregular dense areas in a pale ground-plasm. Some of the forms have dense cytoplasmic bodies which look much like elementary bodies. Others have vacuoles which may contain structures which look like smaller organisms. Especially in older cultures, very large (10 [mu]) vacuolated organisms are seen, probably corresponding to the "large bodies" described by light microscopists. Filamented forms are also seen. These observations suggest several possible modes of reproduction, each perhaps operating under different cultural conditions or at different ages of the culture.