Sedimentation counting and morphology of Mycoplasma

Medium-dependent properties of mycoplasmas

Without a cell wall, the morphology, growth rate, and composition of mycoplasmas are culture media-dependent with variable properties best described as environmentally related. The adaptation of mycoplasmas to either a tissue cell or cell-free culture media, with dependency upon specific animal or plant products for survival, has led to investigations of their human host-related properties. The influence of culture media on the antibiotic sensitivities of mycoplasmas was measured by use of three different broths in two different assay systems. The variable results indicate that the inhibition of mycoplasma protein synthesis or growth may also be host-tissue dependent. The addition of noninhibitory penicillins to different culture media was found to affect the composition and antigenicity of some mycoplasmas. Using the complement fixation test, we found some human sera that were more reactive than rabbit antisera to mycoplasmas cultured in human synovial broth or in myelin-enriched broth. Mycoplasmas cultured in human lung broth and pig lung broth had media-dependent antigenicity. The antigenicity and the growth of mycoplasmas were found to depend on the proteolytic enzymes used to provide the essential peptides in tissue broths. The media-affected mycoplasmas indicate the presence of species-, strain-, and tissue-specific antigen sites that may determine immunopathogenicity in the genetically susceptible host.

Effect of preparatory techniques on the gross morphology of Mycoplasma hominis

A method is presented whereby cells of Mycoplasma hominis can be prepared with minimal distortion for electron microscopy. After the addition of glutaraldehyde to broth cultures, incubation is continued for 1 h. The cells are then collected by centrifugation, washed in distilled water, and used for negative-contrast preparations.

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.

Differential responses of single cells and aggregates of mycoplasms to ultraviolet irradiation

Except for Mycoplasma fermentans strain PG 18, single-cell suspensions of M. arthritidis, M. fermentans (ATCC 19989), M. hominis type 1, M. orale types 1 and 2, M. pneumoniae, and M. salivarium were inactivated exponentially by ultraviolet (UV) irradiation, in contrast to broth cultures containing clusters of elementary bodies. The susceptibility of the mycoplasmas was unaffected by storage at 2-4 C and at -70 C, by sonication, and by filtration. The rate of inactivation was dependent on the intensity of the radiations but independent of the concentration of the cells. Therefore, single-cell suspensions of these mycoplasmas could be differentiated from aggregates of cells by exponential inactivation of the colony-forming units (CFU). By this criterion, the CFU of M. arthritidis in the exponential phase of growth consisted of single cells, in contrast to the other species in which the CFU contained two or more elementary bodies. Even though the cultures of M. fermentans (PG 18) were grown from single cells, they were not homogeneous in their susceptibility to UV light. Neither were cultures of M. arthritidis and M. orale type 1 grown from single cells which had survived irradiation.

Physical properties of human Mycoplasma species

Kim, Kwang S. (University of North Carolina, Chapel Hill), Wallace A. Clyde, Jr., and Floyd W. Denny. Physical properties of human mycoplasma species. J. Bacteriol. 92:214-219. 1966.-Studies were made of the comparative morphology and stability of five Mycoplasma species of human origin (M. hominis type 1, M. salivarium, M. fermentans, M. pneumoniae, M. pharyngis). Broth-cultivated organisms were examined by electron microscopy to determine their relative appearance after uniform processing, including fixation-drying with formaldehyde vapor. M. pneumoniae was characterized by the occurrence of 250- to 300-mmu spheres in clusters, and M. pharyngis by the appearance of filaments 120 mmu by 1.5 to 8 mu; the remaining species revealed a variety of structures, including spheres, rings, and short filaments. To complement these findings, the effect of physical stresses on viability of the mycoplasmas was measured by exposing the organisms to heat (in saline), osmotic variations (in sucrose), and sonic oscillation and repetitive freeze-thawing (in culture medium). M. pneumoniae was most resistant to heat, vibration, and freeze-thawing; M. pharyngis was most sensitive to heart and vibration, but was least affected by osmotic changes. The remaining organisms assumed intermediate positions. The type-related variations in relative morphology and stability suggest differing physical attributes of the mycoplasmas studied, supporting taxonomic differentiation of the five species based on metabolic and immunological criteria.