Iowa State University Veterinarian Records, RS 22/6/0/9, University Archives, Special Collections Department, Iowa State University, http://www.add.lib.iastate.edu/spcl/arch/rgrp/22-6-0-9.html
Mycoplasmas are the smallest organisms (200-300nm) that are capable of growth in cell free medium. They are different from bacteria in that they have no cell walls but are bounded by a unite membrane. The typical mycoplasma colony on solid growth medium has the appearance of a "fried egg." Most mycoplasmas require sterol for growth. Nonsterol requiring mycoplasmas are placed into the genus Acholeplasma.
Kennedy, Sally K.; Gill, Michele; and Farrington, Daniel O.
"Common Swine Mycoplasmas,"
Iowa State University Veterinarian: Vol. 39
, Article 5.
Available at: http://lib.dr.iastate.edu/iowastate_veterinarian/vol39/iss3/5