Infections Due to Species of Mycoplasma and Ureaplasma: An Update

The five genera Mycoplasma, Ureaplasma, Acholeplasma, Anaeroplasma, and Asteroleplasma, within the class Mollicutes (table 1), comprise more than 120 named species. Of these species, most belong to the genus Mycoplasma. The term mycoplasma is often used, as in this review, to refer to any organism within the class, irrespective of genus or species. Mycoplasmas are found mainly in the mouth, the upper respiratory tract, and the more-distal parts of the genitourinary tracts of humans and animals, and the majority of these organisms are host specific. A few undoubtedly cause disease, others are less obviously associated with disease, and many appear to be nonpathogenic. Thirteen Mycoplasma species, two Acholeplasma species, and one Ureaplasma species have been isolated from humans; these species are shown in table 2, together with their respective primary sites of colonization and their metabolic properties. The isolation of a mycoplasma from healthy subjects or animals does not necessarily mean that the organism is merely a commensal; conversely, isolation of a mycoplasma from diseased tissue, particularly when other microorganisms are present, does not prove pathogenicity. The determination that a mycoplasma is a cause of disease in patients or animals should be based on the following factors: (1) the isolation rate among patients or animals with disease is significantly greater than that among those without disease; (2) more organisms of the particular mycoplasmal species are recovered from patients or animals with disease than from those without disease; (3) an antibody response to the mycoplasma occurs in patients or animals with disease, and it occurs significantly more often in them than it does in those without disease; (4) there is a clinical response to an antibiotic to which the mycoplasma is susceptible in vitro, and the response is accompanied by elimination of the mycoplasma; (5) an antibiotic that inhibits the mycoplasma, but not other putative causal agents (a differential antibiotic), produces a beneficial clinical effect; (6) when a mycoplasma of human origin is introduced