Small-subunit rRNA sequences were determined for almost 50 species of mycoplasmas and their walled relatives, providing the basis for a phylogenetic systematic analysis of these organisms. Five groups of mycoplasmas per se were recognized (provisional names are given): the hominis group (which included species such as Mycoplasma hominis, Mycoplasma lipophilum, Mycoplasma pulmonis, and Mycoplasma neurolyticum), the pneumoniae group (which included species such as Mycoplasma pneumoniae and Mycoplasma muris), the spiroplasma group (which included species such as Mycoplasma mycoides, Spiroplasma citri, and Spiroplasma apis), the anaeroplasma group (which encompassed the anaeroplasmas and acholeplasmas), and a group known to contain only the isolated species Asteroleplasma anaerobium. In addition to these five mycoplasma groups, a sixth group of variously named gram-positive, walled organisms (which included lactobacilli, clostridia, and other organisms) was also included in the overall phylogenetic unit. In each of these six primary groups, subgroups were readily recognized and defined. Although the phylogenetic units identified by rRNA comparisons are difficult to recognize on the basis of mutually exclusive phenotypic characters alone, phenotypic justification can be given a posteriori for a number of them.

Adenocarcinoma of the stomach, the second most prevalent of all human malignancies world-wide, is associated with infection at an early age with Helicobacter pylori. Infection leads to several distinctive forms of gastritis, including chronic atrophic gastritis, which is a precursor of adenocarcinoma. H. hepaticus infection in mice constitutes the only other parallel association between a persistent bacterial infection and tumor development known to exist naturally. Study of the H. hepaticus syndrome of chronic active hepatitis and liver tumors in mice may yield insights into the role of H. pylori in human stomach cancer and gastric lymphoma.

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Two hundred throat washings, previously screened and presumed negative for Mycoplasma pneumoniae in conventional mycoplasma culture media, were retested for the organism in a modified medium (PS-4) initially developed for cultivation of a tick-derived Mycoplasma (spiroplasma). The organism was rapidly identified with an agar plate immunofluorescence procedure. M. pneumoniae was isolated from 69 (34.5%) of the 200 "negative" specimens cultured on a diphasic SP-4 medium, in contrast to 10 isolations (5%) made on conventional diphasic mycoplasma medium. This enhanced recovery of M. pneumoniae represented a combination of a superior culture medium and a more efficient identification technique. The findings suggest that these procedures might be effectively applied to the recovery of M. pneumoniae from all likely host and that improved recovery of the organism may aid in the interpretation of a number of puzzling questions about the epidemiology of M. pneumoniae infections.

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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...