GENERAL CHARACTERISTICS OF MYCOPLASMAS: Very small(0.2-0.3 um) . Can pass through bacterial filters. Lack a rigid cell wall. Bound by a single trilaminar cell membrane that contains a sterol. Extremely pleomorphic varying in shape from coccoid to filamentous to other bizzare forms. Mycoplasma, Ureaplasma, Spiroplasma and Anaeroplasma cannot synthesize their own cholesterol and require it as a growth factor in culture medium. Acholeplasma synthesizes carotenol as a substitute for cholesterol, but will incorporate cholesterol if it is provided. Insensitive to cell-wall active antibiotics such as penicillins and cephalosporins. Limited biosynthetic capabilities due to a small genome. Multiply by binary fission. However, cytoplasmic division may lag behind genome division. This results in the formation of multinucleate filaments and other shapes. Do not possess flagellae or pili, but some mycoplasmas including M. pneumoniae, exhibit gliding motility on liquid-covered surfaces. This is attributed to specialized tip structures that also help the organisms in the attachment to the cell. Non sporing Stain poorly with Grams stain. Can be stained with Giemsa and Dienes methods. Are considered as stable L forms by some researchers but this hypothesis is still not fully accepted. Aerobes and facultative anaerobes except Anaeroplasma which is strictly anaerobic. For primary isolation, an atmosphere of 95% Nitrogen and 5% Carbon dioxide is preferred. They can grow within a temperature range of 22-41degC, the parasitic species growing optimally at 35-37degC. For fermentative organisms, the initial pH of the medium is adjusted to 7.3-7.8, for arginine metabolizing organisms it should be around 7 and for ureaplasmas, range of pH should be 6-6.5. PPLO broth/agar and SP4 media are used for isolation of mycoplasmas. Fried egg colony morphology is obtained on culture media. Ref : Textbook of Microbiology by Dr. D.R. Arora; 3rd edition & Mackie McCaney Practical Medical Microbiology; 14th edition