An unusual mycoplasma, which was isolated from the urine of a human immunodeficiency virus-positive male homosexual patient, has an elongated flask shape and two unique sharply divided internal compartments. The tiplike compartment is densely packed with fine granules, and the body compartment is loosely filled with coarse granules consistent with ribosomal structures. The organism has properties of adherence, hemadsorption, and cytadsorption and invades many different types of mammalian cells. Adhesion and penetration apparently involve the terminally located tiplike structure. Cholesterol is required for growth, and the mycoplasma ferments glucose and hydrolyzes arginine, but does not hydrolyze urea. The results of DNA homology studies revealed that this organism is not genetically related to previously described mycoplasma species that have the same biochemical properties. The results of serologic studies demonstrated that this organism is antigenically distinct from all previously described mycoplasmas. We propose that this new mollicute species should be named Mycoplasma penetrans sp. nov. The type strain is strain GTU-54-6A1 (= ATCC 55252).A total of 13 members of the class Mollicutes have been isolated from humans (5, 14, 35). The two most common isolation sites are respiratory and urogenital tracts (5, 3 9 , although isolation from synovial fluids of patients with arthritis (23) and isolation from other anatomical sites have also been reported (15,26,28).The most common mycoplasmas in human urogenital tracts are Mycoplasma hominis and Ureaplasma urealyticum (10, 35). Mycoplasma fernentans, Mycoplasma genitalium, Mycoplasma spermatophilum , Mycoplasma primaturn , Mycoplasma salivarium, and Mycoplasma pneumoniae are less common (5,14,35,37). The frequency of isolation of urogenital mycoplasmas depends in part on the group of individuals studied. Sexual activity, as well as multiple sexual partners, increases the rate of isolation (25). The isolation rates for urogenital mycoplasmas are also different in heterosexual and homosexual males (16).To date, there has been no systematic study of the urogenital mycoplasmas isolated from patients with AIDS. Our previous examination of urine samples from a small number of patients with AIDS in which we used the polymerase chain reaction and cultures for mycoplasmas revealed a high level of M. fermentam infection which was not found in non-AIDS controls (8). In a more comprehensive study, we isolated a previously unknown mycoplasma from urine samples from six patients with AIDS (18). In this paper we describe this organism and its unusual characteristics; we also describe our examination of its distinct biological, serological, and genetic properties, which was carried out in order to establish whether this organism should be given taxonomic status as a new mycoplasma species.* Corresponding author. MATERIALS AND METHODSIsolation and cultivation. SP-4 medium was prepared as described below. A 10-g portion of Tryptone (Difco Laboratories, Detroit, Mich.), 5.3 g of pept...

Antibodies to Mycoplasma penetrans were found at an unusually high frequency in male homosexuals with AIDS (55 of 149; 37%) and in human immunodeficiency virus (HIV)-infected asymptomatic homosexuals (13 of 49; 26.5%) but not in intravenous drug users (3 of 308; 1%) and hemophiliacs (1 of 165; 0.6%) with or without HIV-1 infection. Thus, both M. penetrans and Kaposi's sarcoma (KS) occur primarily in male homosexuals and rarely in other groups of patients at high risk of AIDS. Among 414 HIV-1-infected patients, statistical analysis revealed those with M. penetrans antibody were 11.7 times more likely to develop KS. Furthermore, among 198 HIV-infected homosexuals (149 with AIDS and 49 without AIDS), those with KS had M. penetrans-specific antibody at a significantly higher frequency (28 of 47; 59.6%) than did those without KS (27 of 102 with AIDS [26.5%] as well as 13 of 49 without AIDS [26.5%]; odds ratio = 4.1, P < .001). M. penetrans is apparently transmitted sexually through homosexual activity and is epidemiologically linked to formation of KS in homosexual men with AIDS. Parallel tests with M. genitalium revealed no similar link to KS in the same study sample.