Commentary Mycoplasmas are the smallest free-living organisms. They are distinct from most bacteria because they lack a cell wall and are, thus, not susceptible to antibiotics that act by inhibiting cell wall biosynthesis.
Some strains also require sterols for growth, another unusal property.
Although they are like viruses in that they are filterable, probably because of their plasticity resulting from the lack of a cell wall, they are distinct from viruses in their ability to grow on cell-free media. In contrast to pneumococcal pneumonia that most often infects the elderly, this new disease was reported among adolescents and young adults in boarding schools and military installations. The organism attaches to the ciliated epithelium via a characteristic tip structure. The mycoplasma do not enter the cells but burrow down between them and are found in the intracellular spaces. After attachment there is a decline in protein and RNA synthesis in the host cells, and the cells stop beating.