MYCOPLASMA

            A. CLASSIFICATION

            Kingdom – Bacteria

                  Phylum – Tenericutes  

                        Class – Mollicutes

                               Order Mycoplasmatales

                                      Family – Mycoplasmataceae

                                            Genus – Mycoplasma

            Mycoplasmas are a group of bacteria that are devoid of cell walls and so are highly pleomorphic, with no fixed shape and size. They even lack cell wall precursors like muramic acid or diaminopimelic acid. The cells are bounded by a soft trilaminar unit membrane containing sterols. Because of their plasticity, they can pass through bacterial filters. They are responsible for the cause of disease in many plants and animals and can be obtained from plants, animals, human beings and environmental sources and are called as ‘pleuropneumonia-like organisms’ (PPLO). This name has been replaced by Mycoplasma (Myco, from the fungus like form of the branching filaments; plasma, denoting their plasticity of shape).

            B. MORPHOLOGY

            Shape and size - Mycoplasmas are the smallest free living micro-organisms, and one of the most pleomorphic. They occur as granules and filaments of various sizes. The granules may be coccoid, balloon, disc, ring or star forms. The filaments are slender, of varying lengths and show true branching. A distinctive feature seen in some species is a bulbous enlargement, with a differentiated tip structure, by which the organism get attached to suitable host cells carrying neuraminic acid receptors.

            Mycoplasmas do not posses spores, flagella or fimbria. Some species exhibit a gliding motility. Mycoplasmas are Gram negative but are better stained by Giemsa stain.

            Cell Structure – The cells are small, and the diameter of the cell ranges between 0.3 and 0.9 µm. These are prokaryotes and do not contain true nucleus.

            Each cell is covered with a unit lipoprotein cytoplasmic membrane which is 7.5 – 10 µm thick. The cytoplasm contains genetic material (nucleoplasm like material) and ribosomes. Both DNA and RNA act as genetic material. It is usually half that usually occurs in other prokaryotes. The DNA amounts to 4 percent and RNA about 8 percent. Though gram negative, mycoplasmas stain slowly on long exposure to dyes. Mycoplasmas are non motile but show gliding slow movements. Mycoplasmas are sensitive to streptomycin, erythromycin and chloram phenicol but are insensitive to penicillin.

            C. REPRODUCTION

            Mycoplasmas reproduce by budding and/or binary fission. Cells of mycoplasma divide unevenly into very minute bodies called the elementary bodies or minimal reproductive units. These are formed inside the large bodies or mature cells. Their size varies from 330 nm to 450 nm. These bodies are the smallest independent living entities so far known.

            D. TRANSMISSION

            Mycoplasma like organisms (MLO) or phytoplasma are usually present in the phloem of the host plants and are transmitted from host to another host by leaf hoppers. But some are transmitted by psyllids, treehoppers, plant hoppers and some possibly by aphids and mites. Some of the pathogens are known to infect various organs of their leaf hoppers and psyllid vectors and to multiply in their cells. The vectors cannot transmit in the phytoplasma immediately after feeding on the infected plant, but it begins to transmit after an incubation period of 10 to 45 days depending upon the temperature.

            E. PATHOGENICITY

            Mycoplasma cause two types of disease in humans – pneumonia and genital infections.

            Mycoplasmal pneumonia (primary atypical pneumonia) is caused by M. neumoniae. This disease is typically tracheobronchitis. The disease spread worldwide and is found at all ages. Transmission is by droplets of nasopharyngeal secretion. Spread is favored by close contact with the affected person. The mycoplasma may remain in the throat for two or more months after recovery from the disease.

            Genital infections are caused by M. hominis and U. urealyticum. They are transmitted by sexual contact, and may cause urethritis, proctitis, balanoposthitis and Reiter’s syndrome in menand acute salpigingitis, pelvic inflammatory disease, cervicitis and vaginitis in women. They have also been associated with infertility, abortion, postpartum fever, chrioamnionitis and low birth weight in infants.

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