Clinical Manifestations Clinical ManifestationsClinical Manifestations Clinical Manifestations Clinical Manifestations
Mycoplasma pneumoniae infection is a disease of the upper and lower respiratory tracts. Cough, fever, and headache may persist for several weeks. Convalescence is slow. Ureaplasma urealyticum infection causes nongonococcal urethritis in men, resulting in dysuria, urgency, and urethral discharge.
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Mycoplasmas are spherical to filamentous cells with no cell walls. There is an attachment organelle at the tip of filamentous M pneumoniae, M genitalium, and several other pathogenic mycoplasmas. Fried-egg-shaped colonies are seen on agar. The mycoplasmas presumably evolved by degenerative evolution from Gram-positive bacteria and are phylogenetically most closely related to some clostridia. Mycoplasmas are the smallest self-replicating organisms with the smallest genomes (a total of about 500 to 1000 genes); they are low in guanine and cytosine. Mycoplasmas are nutritionally very exacting. Many require cholesterol, a unique property among prokaryotes. Ureaplasmas require urea for growth, another unusual property. Mycoplasmas have surface antigens such as membrane proteins, lipoproteins, glycolipids, and lipoglycans. Some of the membrane proteins undergo spontaneous antigenic variation. Antibodies to surface antigens inhibit growth; various serological tests have been developed and are useful in classification.
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Mycoplasmas are surface parasites of the human respiratory and urogenital tracts. Mycoplasma pneumoniae attaches to sialoglycoproteins or sialoglycolipid receptors on the tracheal epithelium via protein adhesins on the attachment organelle. The major adhesin is a 170-kilodalton (kDa) protein, named P1. Hydrogen peroxide and superoxide radicals (O2–) excreted by the attached organisms cause oxidative tissue damage. Pneumonia is induced largely by local immunologic and phagocytic responses to the parasites. Sequelae of M pneumoniaeCopyright © 1996
The University of Texas Medical Branch at Galveston