Physical properties of human Mycoplasma species

New type of encephalomyelitis responsive to trimethoprim/sulfamethoxazole treatment in Japan

Objective:

To determine the causative pathogen and investigate the effective treatment of a new type of encephalomyelitis with an unknown pathogen in Japan and report the preliminary ultrastructural and genomic characterization of the causative agent.

Methods:

From 2005 to 2012, we treated 4 Japanese patients with geographic clustering and comparable clinical features, serum/CSF cytology, and radiologic findings. Brain biopsy was conducted in all patients to analyze neuropathologic changes by histology, and electron microscopy was applied to reveal the features of the putative pathogen. Genomic DNA was obtained from the affected brain tissues and CSF, and an unbiased high-throughput sequencing approach was used to screen for specific genomic sequences indicative of the pathogen origin.

Results:

All patients exhibited progressive dementia with involuntary tongue movements. Cytologic examination of CSF revealed elevated mononuclear cells. Abnormal MRI signals were observed in temporal lobes, subcortical white matter, and spinal cord. Biopsied brain tissue exhibited aggregated periodic acid-Schiff–positive macrophages and 2–7 μm diameter round/oval bodies without nuclei or cell walls scattered around the vessels. Unbiased high-throughput sequencing identified more than 100 archaea-specific DNA fragments. All patients were responsive to trimethoprim/sulfamethoxazole (TMP-SMX) plus corticosteroid therapy.

Conclusions:

We report 4 cases of encephalomyelitis due to an unknown pathogen. On the basis of ultrastructural and genomic studies, we propose a new disease entity resulting from a causative pathogen having archaeal features. TMP-SMX therapy was effective against this new type of encephalomyelitis.

Induction of macrophage-mediated cytolysis of neoplastic cells by mycoplasmas

Unexpected cytolysis was encountered when nonactivated murine peritoneal macrophages were cultured with [3H]TdR-prelabeled syngeneic or allogeneic tumor cells at a 10:1 ratio. The level of specific cytolysis reached 70% within 48 hr of cocultivation. Similar killing was observed whether the macrophages were derived from untreated, thioglycollate-treated, or germ-free mice. Cytolytic activity was also demonstrated when bone marrow-derived or peritoneal macrophages from 9- and 5-day in vitro cultures, respectively, were employed rather than freshly harvested peritoneal macrophages. Thus, the macrophage-mediated killing was neither the result of in vivo preactivation nor a consequence of the presence of lymphocytes in the assay. Moreover, macrophages derived from different strains caused similar effects. Our study revealed that the neoplastic target cell cultures susceptible to cytolysis by nonactivated macrophages were contaminated with mycoplasma. A mycoplasma was isolated from the supernatant of a culture of the A9HT fibrosarcoma line, identified as Mycoplasma orale, and cultivated. Addition of viable mycoplasma from that isolate to mixed cultures of thioglycollate-elicited macrophages and [3H]TdR-prelabeled mycoplasma-free target cells resulted in specific cytolysis of transformed A9 cells, but not of normal mouse fibroblasts. The level of macrophage-dependent cytolysis correlated with the number of viable mycoplasma cells added and was higher than that attained by activation with LPS at optimal concentration. Similar specific cytolysis was observed with heat-killed mycoplasmas. Our results demonstrate that mycoplasmas may cause selective macrophage-mediated cytolysis of neoplastic but not of normal target cells, perhaps via activation of the macrophages. It is suggested that undetected infection of experimental systems by mycoplasmas may account for some reports on lysis of neoplastic cells by nonactivated macrophages.

Inactivation of mycoplasma in serum with binary ethyleneimine

A method of inactivating mycoplasma contaminants in sera by using binary ethyleneimine was tried. When used at the concentration recommended for inactivating viruses, 0.001 M, binary ethyleneimine inactivated only two of five mycoplasma species. Even at a concentration of 0.01 M, the compound did not consistently inactivate all mycoplasmas.

Cold hemagglutinin cross-reactivity with Mycoplasma pneumoniae

Convalescent sera from proven cases of infection with Mycoplasma pneumoniae, and rabbit antisera to M. pneumoniae and to human erythrocyte glycoprotein contained cold hemagglutinins which were reactive only for human erythrocytes. Only the human serum cold agglutinins were inhibited by soluble integral glycoproteins derived from human erythrocyte ghosts by treatment with chloroform-methanol. Rabbit antiserum to chloroform-methanol glycoprotein, as well as to M. pneumoniae, fixed complement with either M. pneumoniae or chloroform-methanol glycoprotein antigens. The findings support the hypothesis that the cold agglutinins elicited by M. pneumoniae infection represent a cross-reaction between determinants common to erythrocyte glycoprotein containing I antigen and the membrane of M. pneumoniae.

Morphology and ultrastructure of Mycoplasma pneumoniae spherules

During growth in fluid medium, most strains of Mycoplasma pneumoniae produce free-floating granules which become larger with time. We have called these granules "spherules." This study describes the morphological and ultrastructural features of M. pneumoniae strain AP-164 spherules, both free and in association with HeLa cells in cell culture. In thin section, spherules were composed of lobulated cells, connected together by membranes, and ring-shaped cells. The two-dimensional morphology observed varied according to the plane of section and to the age of the culture. In HeLa cell cultures, mycoplasmata were found attached to plasma membranes of cells; in sections, individual mycoplasmata were often aligned in radial apposition to the membranes. Mycoplasmata were not found intracellularly. The three-dimensional morphology of spherules was examined by the critical point method and by scanning electron microscopy. Both methods revealed lobulated forms, ring-shaped forms, and star-shaped forms. Treatment of the spherules with crude porcine pancreatic lipase effectively released large numbers of free organisms. Phosphotungstic acid preparations of these uncentrifuged forms revealed a morphology in agreement with the other methods used. Lobulated ring forms with "beaded" filaments were prominent. In respect to morphology, M. pneumoniae under our conditions resembles that of the type species M. mycoides.

Relationships Between Mycoplasma pneumoniae and Human Respiratory Epithelium

The interaction was studied between Mycoplasma pneumoniae and its natural host cell, the human respiratory epithelium. Organized, ciliated cells provided by fetal trachea in organ culture enabled examination of the host-parasite relationship by light, immunofluorescence, and electron microscopy. Impairment of cellular function was reflected by disorganization and loss of ciliary motion; this was associated with a sequence of cytopathological changes denoting progressive cell injury. The organisms were found concentrated on the luminal surface of ciliated epithelium and cells lining the submucosal glands. A differentiated portion of the Mycoplasma, consisting of an extension of the unit membrane containing an electron-dense core surrounded by a lucent space, served as the means of attachment to host cells. The findings suggest that the pathogenicity of M. pneumoniae depends upon intimate extracellular infection with production of functional and structural changes initiated by host cell membrane injury.

Ultrastructural features of Mycoplasma pneumoniae

The ultrastructure of Mycoplasma pneumoniae cultivated in broth on glass and plastic surfaces was studied by scanning and transmission electron microscopy. The organisms grew as filaments, which by over-crossing eventually formed a dense network on the surface and in colonies composed mainly of rounded and elongated forms. The filaments were usually thinner at the ends and terminated with a knob-like structure. Some filaments possessed short ramifications which also ended with a knob, and others showed constrictions. Sectioned organisms were seen to contain ribosome-like structures. Many organisms had a specialized structure at their thinner end, which consisted of a dense rod surrounded by electron-lucent cytoplasm and ending with a platelike thickening.

Three-dimensional morphology, ultrastructure, and replication of Mycoplasma felis

The morphology and replication of Mycoplasma felis in relation to growth phase in culture were studied by electron microscopy. The organisms showed 1.0 to 1.45-hr doubling times with typical bacterial-type growth curves when grown in dialysate broth supplemented with horse serum. Organisms were fixed for electron microscopy by using Veronal acetate-buffered 0.8% OsO(4) (pH 6.1) in 20% sucrose. The morphology of exponential-phase organisms differed markedly from that of stationary or death-phase organisms, which were essentially large round forms with either dispersed or abnormally aggregated cytoplasm. Plasticine models prepared from serial sections of organisms in exponential phase showed the organisms to be either disc-shaped, triangular, horseshoe-shaped, or multilobular. A central "hole" was frequently present in these structures and could be visualized in the lobular forms as an interconnecting circular membrane. The inner surface of this membrane often showed contact with a small membranous body about 0.12 mum in diameter. The significance of this body is unknown. The morphology of the various shapes was confirmed by using the phosphotungstic acid and critical point methods. When the ratios of the various forms in exponential-phase cultures were determined, it was found that a replication sequence could be proposed which accounted for not only the volume increase required to accommodate deoxyribonucleic acid (DNA) replication but also the distribution of that DNA. Although it is likely that DNA replication in M. felis is a binary process, it appears that the mechanism for production of new cells need not be a binary process.

The antigens of Mycoplasma hominis

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Characteristics of virulent, attenuated, and avirulent Mycoplasma pneumoniae strains

Homologous pairs of virulent and attenuated or avirulent Mycoplasma pneumoniae strains were derived and compared in an effort to elucidate the mechanisms of virulence. These related strains were found to vary in growth, glycolysis, protein electrophoretic patterns, peroxide formation, morphology, and cytadsorption. Variations in the last two characteristics closely correlated with avirulence. This enables understanding of one stage in the pathogenic sequence and provides a convenient marker for avirulence. The derivation of infectious avirulent strains may make possible their use as live vaccines against M. pneumoniae disease.

Role of relative humidity in the survival of airborne Mycoplasma pneumoniae

Aerosols of Mycoplasma pneumoniae were studied at several relative humidities at a controlled temperature of 27 C. Production of an experimentally reproducible aerosol required preatomization of the organism in its suspending fluid and was dependent on the type of fluid used in atomization as well as on the procedures used to produce an aerosol. The airborne particles studied were within the range of epidemiological significance, with most being 2 mum or less in diameter. Survival of the airborne mycoplasma in these particles was found to be best at very low and at very high humidities. The most lethal relative humidity levels were at 60 and 80%, at which levels fewer than 1% of the organisms survived over a 4-hr observation period. However, survival of the organism at most relative humidity levels was such that long-term infectivity could be expected from aerosols of M. pneumoniae. Because of the extreme sensitivity of M. pneumoniae at critical humidity levels, control of the airborne transmission of these organisms may be possible in selected spaces.