Mycoplasmas and cell cultures

Adenosine phosphorylase activity in a mutant HEp-2 cell line contaminated with Mycoplasm hyorhinis

Metabolic studies in HEp-2/MP,MIR cells (an adenosine kinase, hypoxanthine phosphoribosyltransferase negative mutant) indicated the presence of adenosine phosphorylase activity. This activity, unknown in established mammalian cell lines, resulted in the glycosidic cleavage of both adenosine and the antiviral drug arabinosyladenine. The activity was observed readily in the presence or absence of the adenosine deaminase inhibitor conformycin. Isopycnic separation of [3H] thymidine-labeled DNA species in CsCl density gradients resulted in the appearance of two distinct peaks. The heavier peak coincided with [14C]thymidine-labeled marker DNA of human origin, whereas the lighter peak was within the range associated with mycoplasmal DNA. Testing by commercial laboratories confirmed the presence of mycoplasma in HEp-2/MP,MIR cells. The contaminant was identified as Mycoplasma hyorhinis, a porcine mycoplasma. Following gamma-irradiation (3000 rads) to block cellular mitosis, the mucoplasma-contaminated HEp-2/MP,MIR cells were cocultivated with mycoplasma-free wild-type HEp-2 cells which did not exhibit adenosine phosphorylase activity. Following serial cocultivation in a medium designed to favor the survival of the wild-type cells, adenosine phosphorylase activity was found in the previously uninfected cells. Studies of this nature emphasize the need for investigators to carefully monitor their cell lines for mycoplasma.

Mycoplasma in African green monkey kidney cell cultures: biochemical detection and effects in virus-infected cells

Among a number of techniques for the detection of mycoplasmal contamination in African green monkey kidney (AGMK) cell lines, the assay of uridine phosphorylase activity is unsuitable because of the presence of high levels of endogenous enzymatic activity. A thymidine phosphorylase test, however, based on the chromatographic analysis of radiolabeled thymidine breakdown, turned out to be a simple and sensitive mycoplasma detection method. We found, using the latter technique, that 0.22-micrometer-filtered virus inocula could still transfer mycoplasma unless treated with diethyl ether. The effect of mycoplasmal contamination on the synthesis of simian virus 40 and adenovirus in AGMK cells was negligible under the conditions used (no depletion of arginine). Incorporation of radioactive thymidine in viral macromolecules, however, was inhibited severely by the presence of mycoplasma.

Effect of squamous metaplasia on infection of hamster trachea organ cultures with Mycoplasma pneumoniae

An organ culture system for hamster trachea was developed for maintenance of the ciliated respiratory epithelium during periods of extended cultivation (i.e., greater than 20 days). Evaluation of five serum types showed that horse serum and fetal calf serum were best for the maintenance of epithelial ciliary activity and morphology. Rings that were opened on one side ("split rings") had the best maintenance of the ciliated epithelium as judged by the retention of ciliary activity and normal histological appearance after 3 to 4 weeks in culture. The in vitro induction of squamous metaplasia was achieved by cultivating explants in Waymouth MAB 87/3 (vitamin A-free) medium, without serum. This system allowed a direct comparison of the effects of Mycoplasma pneumoniae infection in two epithelial types, ciliated pseudostratified columnar and keratinizing squamous. Attachment of 14C-labeled mycoplasmas was more than twofold greater in the normal epithelium. Pretreatment of explants with neuraminidase decreased attachment for both squamous and pseudostratified epithelial surfaces to a similar basal level. Recovery of viable organisms from infected tissue of both epithelial types indicated that the organism titer remained essentially constant during the infection period, but was significantly higher for the pseudostratified ciliated epithelium. These results suggest that specific receptor sites for M. pneumoniae are markedly reduced by the induction of squamous metaplasia and, hence, appear to be specific for the normal respiratory surface containing goblet cells and pseudostratified, ciliated epithelial cells.

Prolonged eradication of urogenital mycoplasmas after administration of tetracycline to men in the Antarctic

Meatal swabs were obtained at intervals over 1 year from 23 men in the Antarctic. A 5-day course of tetracycline was given to twelve of them. In retrospect it was found that the antibiotic had been received by two men who were harbouring ureaplasmas, one of whom also had M. hominis. After treatment, these organisms were not found in any of the swabs taken over the next year, except in a swab from one of the men following sexual contact after this time. One of the twelve men developed N.S.U. just before arriving in the Antarctic. He responded clinically to a shorter course of tetracycline and ureplasmas were not recovered from a meatal swab immediately thereafter. However, without further sexual contact, ureaplasmas and disease recurred about a month later. This time, after a 5-day course of tetracycline, disease was not seen, and ureaplasmas were not isolated, over the next year. In contrast, ureaplasmas were isolated consistently over a year from two men who were not given the antibiotic. The evidence strongly suggests that, under natural conditions, the most likely cause of mycoplasmas, particularly ureaplasmas, recurring in the genital tract after apparently adequate tetracycline therapy, is re-infection as a result of sexual re-exposure.

Ultrastructural visualization of anionic sites on mycoplasma membranes by polycationic ferritin

Anionic sites on mycoplasma membranes were visualized in the electron microscope by a polycationized ferritin derivative. The technique of thin sectioning was used. Staining prior to fixation led to clustering of ferritin granules on the mycoplasma cell surface. On glutaraldehyde-fixed Mycoplasma mycoides subsp. capri, M. gallisepticum, M. pneumoniae, and Acholeplasma laidlawii, the anionic sites were uniformly distributed over the entire membrane surface. M. hominis did not bind the polycationic ferritin label. Chemical and enzymatic treatments of the mycoplasmas indicated that the anionic sites may be lipid phosphate groups. Isolated M. mycoides subsp. capri membranes were labeled exclusively on only one membrane surface, presumably the outer one. Liposomes prepared from diphosphatidylglycerol and phosphatidylcholine were also labeled by the polycationic ferritin.

Mycoplasma-mediated hyporeactivity to various interferon inducers

Three strains of Mycoplasma arthritidis were shown to induce marked hyporeactivity in mice to interferon induction by both Newcastle disease virus and poly(I:C). In contrast, the interferon response of mice to tilorone was only partially suppressed by pretreatment of the animals with mycoplasms. Hyporeactivity to Newcastle disease virus was maximal 1 and 3 days after mycoplasms treatment, but the interferon response was maximal 1 day after injection of the mycoplasmas and was no longer apparent by 5 days. No relationship was found between the ability of the mycoplasms themselves to induce interferon and the degree of hyporeactivity produced. These results suggest that mycoplasmas may alter virus-host relationships in vivo.

Adenine formation from adenosine by mycoplasmas: adenosine phosphorylase activity

Mammalian cells have enzymes to convert adenosine to inosine by deamination and inosine to hypoxanthine by phosphorolysis, but they do not possess the enzymes necessary to form the free base, adenine, from adenosine. Mycoplasmas grown in broth or in cell cultures can produce adenine from adenosine. This activity was detected in a variety of mycoplasmatales, and the enzyme was shown to be adenosine phosphorylase. Adenosine formation from adenine and ribose 1-phosphate, the reverse reaction of adenine formation from adenosine, was also observed with the mycoplasma enzyme. Adenosine phosphorylase is apparently common to the mycoplasmatales but it is not universal, and the organisms can be divided into three groups on the basis of their use of adenosine as substrate. Thirteen of 16 Mycoplasma, Acholeplasma, and Siroplasma species tested exhibit adenosine phosphorylase activity. M. lipophilium differed from the other mycoplasmas and shared with mammalian cells the ability to convert adenosine to inosine by deamination. M. pneumoniae and the unclassified M. sp. 70-159 showed no reaction with adenosine. Adenosine phosphorylase activity offers an additional method for the detection of mycoplasma contamination of cells. The patterns of nucleoside metabolism will provide additional characteristics for identification of mycoplasmas and also may provide new insight into the classification of mycoplasmas.

Comparison of methods for the detection of Mycoplasmal contamination of cell cultures: a review

Several reviews in recent years have emphasized the problems created by mycoplasmal contamination of cultured cells (1-5). Because of the hazards of interpreting data derived from mycoplasma contaminated cells, most cell biologists routinely screen their cultures for the presence of these organisms. In recent years, the limitations of standard microbiological testing for mycoplasmas have become increasingly apparent and have led to the development of several new biochemical techniques for detection of these organisms. The aim of this review is to describe and compare available detection techniques and to evaluate their relative efficacy. Those properties of mycoplasmas that are relevant to their role as cell culture contaminants will be briefly discussed.

Isolation of Acholeplasma laidlawii from commercial, serum-free tissue culture medium and studies on its survival and detection

This report documents the first isolation of Acholeplasma laidlawii from a commercial lot of serum-free Dulbecco basal medium. Experimental studies demonstrated survival of the organism for at least 1 year depending on the concentration of the contaminating organism as well as pH and temperature of storage of the serum-free medium. A comparison of isolation methods showed that concentration by filtration through 220-nm membrane filters and testing the filters for mycoplasma recovery, especially when using phenol red-diphasic Hayflick medium, was both sensitive and practical for the average laboratory.

Mycoplasma contamination of cultured amniotic fluid cells: potential hazard to prenatal chromosomal diagnosis

Amniotic fluid cell cultures were screened for mycoplasma contamination. Mycoplasma RNA's were observed in more than half the cultures examined. Karyotypic analyses of these contaminated cell cultures revealed a significant increase in chromosomal aberrations. These studies emphasize the need for screening for mycoplasma in cultured amniotic cells.

Interaction of mycoplasmas with cell cultures, as visualized by electron microscopy

Mycoplasmas were examined on the surfaces of tissue culture cells prepared for transmission and scanning electron microscopy. The pleomorphic bodies seen were proved to be mycoplasmas by the use of thin sections, passage of the infection from one cell line to another, and by autoradiography with [(3)H]thymidine both on the sections and the replicas. The mycoplasmas were not always evenly distributed over the cell's surface; their arrangement seemed to correlate with the activity or morphology of the cell. The use of replicas and scanning electron microscopy in routine examination of cultures for mycoplasma contamination is discussed.

Search for mycoplasma in synovial fluids from patients with rheumatoid arthritis

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Mycoplasma-associated induction of interferon in ovine leukocytes

A mycoplasmal species, Acholeplasma laidlawii, isolated as a contaminant from a fetal lamb kidney cell line, was shown to be associated with the induction of interferon in cultures of ovine peripheral blood leukocytes. Broth cultures of the mycoplasma induced between 20 and 230 U of interferon per ml in leukocytes from two adult ewes. The amount of interferon produced correlated with the inoculum size of mycoplasma. Interferon production was associated with replication of the mycoplasma in the leukocyte cultures. Interferon was not induced by sterile mycoplasmal broth, a cell-free filtrate of the mycoplasmal cultures, or heat-inactivated mycoplasmas. The antiviral substance was characterized as interferon by the usual criteria.

Experimental Mycoplasma pulmonis infection in pathogen-free mice. Models for studying mycoplasmosis of the respiratory tract

Mice of a Swiss substrain, reared under rigid pathogen-free (PF) conditions, were inoculated intranasally with broth cultures of Mycoplasma pulmonis ranging in dose from 10(1) to 9 x 10(9) colony forming units (CFU). A highly reproducible disease resulted with an LD(50) of 1.3 x 10(8) CFU and a PD(50) (dose producing pneumonia in 50% of mice) of 3.4 x 10(5) CFU. The inoculating dose of M pulmonis was found to be the critical determinant of the severity, duration and pathologic character of the respiratory disease produced. PF mice given 10(4) CFU or less developed a transient illness characterized by low frequencies of rhinitis, otitis media, laryngotracheitis and focal pneumonia. This was proposed as a low dose model. Doses of 10(5) to 10(9) CFU resulted in high frequencies of rhinitis, otitis media, laryngotracheitis and pneumonia. Within the first 10 days the pneumonia often was fatal, being characterized by an outpouring of neutrophils and edema fluid into alveolar spaces, pulmonary congestion and hemorrhage and, occasionally, pleuritis. This high dose-acute disease model was shown to be the result of seeding alveoli with large numbers of organisms at the time of intranasal inoculation. In animals surviving doses of 10(5) to 10(9) CFU beyond approximately 10 days postinoculation, the larger concentration of organisms was present in bronchi and bronchioles, giving rise to a third model, the high dose-chronic disease model. The predominant lesions were chronic suppurative bronchitis and bronchiolitis, marked peribronchial lymphoid cuffing, variable numbers of neutrophils and macrophages in alveoli, and complications such as bronchiectasis and pulmonary abscesses. Identical lesions were observed in axenic mice infected with M pulmonis. The infection in PF mice is considered a highly useful experimental system, both for comparative study of respiratory mycoplasmosis and for investigations directed toward understanding and eliminating the natural disease this agent causes in conventional mice and rats.

Interaction of Mycoplasma arthritidis and other mycoplasmas with murine peritoneal macrophages

Neither mouse nor rat peritoneal macrophages were able to kill Mycoplasma arthritidis to any observable degree in the absence of specific hyperimmune rabbit antiserum. Although convalescent mouse and rat serum were somewhat inhibitory to M. arthritidis in the absence of macrophages, these sera did not promote active phagocytosis by peritoneal macrophages. In fact, the macrophages appeared to protect the mycoplasmas against the inhibitory effects of the antisera by stimulating their growth. Hyperimmune rabbit antiserum against M. arthritidis initiated phagocytic action and resulted in a 50-fold decrease in numbers of viable mycoplasmas by 6 h. In contrast with M. arthritidis, M. pulmonis rapidly adsorbed to the surface of peritoneal macrophages. Upon addition of specific rabbit antiserum, a rapid decrease in viable organisms occurred, and a more complete destruction of organisms ensued in comparison with M. arthritidis. M. gallinarum, as with M. arthritidis, did not adsorb to the macrophages to any great extent. Phagocytic action was observed only in the presence of homologous rabbit antiserum and was not marked until after 6 h of incubation.

Cell biology of the mycoplasmas

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