21Vol. 3, No. 1—January-March 1997 Emerging Infectious Diseases Synopses

No other group of procaryotes has been so embroiled in controversy and in establishing a clear pathogenic niche as the mycoplasmas. Their virulence determinants are undeniably complex, and their unique biological properties likely chal-lenge the host differently from typical bacterial pathogens (1,2). Also, numerous Mycoplasma species appear to comprise the commensal micro-bial flora of healthy persons (3), and the association of these mycoplasmas with disease complicates the diagnosis and necessitates extensive and highly specific serologic, nucleic acid, and epide-miologic data. Nonetheless, mycoplasmas by themselves can cause acute and chronic diseases at multiple sites with wide-ranging complications and have been implicated as cofactors in disease. Recently, mycoplasmas have been linked as a cofactor to AIDS pathogenesis and to malignant transformation, chromosomal aberrations, the Gulf War Syndrome, and other unexplained and complex illnesses, including chronic fatigue syn-drome, Crohn’s disease, and various arthritides (4-8). Even with mounting evidence of their pervasive and pathogenic potential, mycoplasmas still evoke the image of a group of obscure or impotent microorganisms. Yet they are evolu-tionarily advanced procaryotes (9-11), and their elite status as “next generation ” bacterial patho-gens necessitates new paradigms in fully under-standing their disease potential. Mycoplasmas, which lack cell walls but possess distinctive sterol-containing plasma mem-branes, are taxonomically separated from other bacteria and belong to the class Mollicutes (mollis, soft; cutis, skin). Mollicutes, a term that includes the cell wall-less procaryotes assigned to numerous genera under the class Mollicutes and is frequently used interchangeably with myco-plasmas, are unusual for other biological reason