Comparative studies between microbiological culture and uptake of uridine/uracil to detect mycoplasmal infection of cell cultures

Mycoplasma infection followed by time-lapse microscopy

Early detection of mycoplasma infection is crucial for saving precious often irreplaceable data from the tissues of patients. Mycoplasma infections cause diseases in the upper and lower respiratory tracts, urethritis in men resulting in painful dysuria, urgency and urethral discharge. Cough, fever, headache, urethritis may persist for several weeks and convalescence is slow. The symptoms of these diseases are aggravated by the detection of mycoplasma infections, that takes either a long time, besides being expensive or is specific and restricted to only a limited number of contaminant strains. Mycoplasmas are hard to detect visually but could be seen and followed by time-lapse microscopy. Our hypothesis is that one can detect mycoplasma infection irrespective of its origin and type of mycoplasma. Main lines of supporting evidence are provided by the time-lapse microscopy showing dynamic morphological alterations caused by mycoplasmas before changes in human cell cultures become visible. Morphometric measurements of mycoplasma infections revealed four subphases: i) detachment of infected cells, ii) aggregation, iii) biofilm formation and iv) shrinkage of infected cells. The applicability of time-lapse microscopy for the detection of mycoplasma infection was validated by a mycoplasma test Kit. Most important implications related to morphometric parameters include the observation of mycoplasma infected cultures for an extended period of time instead of applying static snap-shot microscopy. A reliable method is offered to estimate the time of mycoplasma exposure that elapsed during the cell growth. This microphotometric approach served a more economical detection of mycoplasma contamination at its early stage of cell growth and spread, irrespective of the origin of contaminated serum, without defining the type of mycoplasma.

Mycoplasma contamination alters 2'-deoxyadenosine metabolism in deoxycoformycin-treated mouse leukemia cells

Deoxycoformycin-treated P388 and L1210 mouse leukemia cells salvage 2'-deoxyadenosine from the medium only inefficiently, because deoxyadenosine deamination is blocked and its phosphorylation is limited by feedback controls. Mycoplasma contamination at a level that had no significant effect on the growth of the cells increased the salvage of deoxyadenosine greater than 10 fold over a 90 min period of incubation at 37 degrees C, but in this case deoxyadenosine was mainly incorporated into ribonucleotides and RNA via adenine formed from deoxyadenosine by mycoplasma adenosine phosphorylase. Deoxyadenosine was an efficient substrate for this enzyme, in contrast to 2',3'-dideoxyadenosine which was not phosphorolyzed. Mycoplasma infection was confirmed by the presence of uracil phosphoribosyltransferase activity and by culture isolation. The contaminant has been identified as Mycoplasma orale. Mycoplasma infection had no effect on the deamination and phosphorylation of deoxyadenosine and adenosine, on the salvage of hypoxanthine and adenine, or on the degradation of dAMP and dATP by the cells or on their acid and alkaline phosphatase activities.

Macrophage colony-stimulating activity is produced by three different EBV-transformed lymphoblastoid cell lines

The lymphoblastoid cell lines BLY 9.84, Gl, and Pl constitutively release a colony-stimulating activity (CSA) which specifically stimulates murine macrophage progenitor cells in vitro. The biochemical characterization of BLY 9.84-derived CSA exhibits a molecular size of apparently 150-200 kDa even under dissociating conditions with 6 M guanidine hydrochloride or inhibition of glycosylation. Production of this CSA is inhibited by cycloheximide and its activity is destroyed by reduction with dithiothreitol. Replating experiments give evidence for a functional similarity with CSF-1 (macrophage colony-stimulating factor).

Junctional transfer in cultured vascular endothelium: II. Dye and nucleotide transfer

Vascular endothelial cultures, derived from large vessels, retain many of the characteristics of their in vivo counterparts. However, the observed reduction in size and complexity of intercellular gap and tight junctions in these cultured cells (Larson, D.M., and Sheridan, J.D., 1982, J. Cell Biol. 92:183) suggests that important functions, thought to be mediated by these structures, may be altered in vitro. In our continuing studies on intercellular communication in vessel wall cells, we have quantitated the extent of junctional transfer of small molecular tracers (the fluorescent dye Lucifer Yellow CH and tritiated uridine nucleotides) in confluent cultures of calf aortic (BAEC) and umbilical vein (BVEC) endothelium. Both BAEC and BVEC show extensive (and quantitatively equivalent) dye and nucleotide transfer. As an analogue of intimal endothelium, we have also tested dye transfer in freshly isolated sheets of endothelium. Transfer in BAEC and BVEC sheets was more rapid, extensive and homogeneous than in the cultured cells, implying a reduction in molecular coupling as endothelium adapts to culture conditions. In addition, we have documented heterocellular nucleotide transfer between cultured endothelium and vascular smooth muscle cells, of particular interest considering the prevalence of "myo-endothelial" junctions in vivo. These data yield further information on junctional transfer in cultured vascular endothelium and have broad implications for the functional integration of the vessel wall in the physiology and pathophysiology of the vasculature.

Elimination of Mycoplasma orale from the human hepatoma cell line, PLC/PRF/5

We have tried without success to eliminate M. orale from a human hepatoma line, PLC/PRF/5, using five different methods. We report here the successful elimination of the contamination by a modification of the technique of Marcus et al. [1] using 5-bromodeoxy-uridine (BrdU) instead of 5-bromo-uracil (5-BrUra) and light. We believe that this method may prove useful when rare and valuable cell lines carry the more common mycoplasma contaminant M. orale.

Mycoplasmal infection of insect cell cultures

Twenty-five cell cultures of three insect orders from eight laboratories were tested for mycoplasmal infection. Acholeplasma laidlawii was detected in one culture, an incidence of 4.0%. A. laidlawii, Mycoplasma orale, M. arginini, but not M. hyorhinis, could establish infections of drosophila Dm-1 cell cultures at 25 degrees C. In prospective studies, drosophila Dm-1 cultures were intentionally infected with broth-propagated A. laidlawii and M. hyorhinis. M. hyorhinis did not grow and was eliminated from the Dm-1 cultures during consecutive passages. A. laidlawii grew without obvious cytopathic effects during six weekly passages; titers of over 10(7) CFU/ml were recorded at Passages 2 and 5 (p2 and p5). Minimal cell culture infectious doses were also determined during these studies. 0.1 milliliter cell samples were inoculated into Leighton tubes containing either fresh M1A culture medium or 3T6 indicator cells in McCoy's 5a medium. After 4 d of incubation at 25 and 37 degrees C, respectively, the cover slips were stained by DNA fluorochrome Hoechst 33258 (A. laidlawii) or by specific fluorescein-conjugated antiserum (M. hyorhinis). At p2 with both mycoplasma species, the procedure using M1A medium and incubation at 25 degrees C without 3T6 cells was inferior to indicator cells. In five of six experiments at least a two-log higher titer of mycoplasmas was needed to be detected with M1A and 25 degrees C. At p5 no difference could be found. Uridine phosphorylase assays of Dm-1 cultures infected with A. laidlawii, M. hyorhinis, M. orale, and M. arginini gave clearly positive results only with A. laidlawii. The ratio of incorporated uridine to incorporated uracil method yielded false positives with two drosophila cell lines. Suggestions for assay of mycoplasmas in invertebrate cell cultures are given.

Cyanide insensitive respiration in mammalian cells: an artifact of mycoplasmal contamination

Oxygen consumption by mammalian cells occurs primarily in the mitochondria although alternate oxidation pathways are also present. The resistance (often high) of these alternate pathways to metabolic inhibitors like CN- determine the residual oxygen consumption in the presence of the inhibitor. In many plant cells and micro-organisms the cyanide insensitive pathway can account for an appreciable fraction of the total oxygen consumption. We were studying oxidation by electron-affinic drugs in nonmitochondrial pathways and were surprised to find some mammalian cell lines having 10% - 90% residual oxygen consumption in the presence of 1 mM CN-. This oxygen consumption was associated with mycoplasmal contaminants (Mycoplasma hyorhinis, Mycoplasma arginini) and disappeared after treatment with appropriate antibiotics. The rate of CN- insensitive oxygen consumption was dependent on the mammalian cell concentration suggesting that the organisms were oxidizing a product of the mammalian cells. In one species (Mycoplasma hyorhinis) lactate may be the oxidative substrate. Mycoplasmas are known to cause a large number of metabolic alterations in their mammalian cell hosts (Stanbridge et al, 1978) sometimes indirectly due to the metabolism of microorganisms themselves, and sometimes directly due to interference with the normal metabolism of the mammalian cells. It is also known that the respiratory pathways of mycoplasmas are vastly different from those of mammalian cells, (Van Demark and Smith, 1964; see Pollack, 1980 for review) and one might expect alterations of the overall respiratory patterns between infected and non-infected mammalian cell-cultures.(ABSTRACT TRUNCATED AT 250 WORDS)

An autoradiographic method of detecting A. laidlawii and M. hyorhinis in cell cultures

The autoradiographic investigation of L cells and chinese hamster cells for the presence of mycoplasmas (A. laidlawii and M. hyorhinis) using uridine/uracil (UdR/U) testing is a rapid and reliable method suitable for the serial checking of even a small number of cells. It depends on a reduced incorporation of [3H]uridine and an increased uptake of [3H]uracil into the RNA of mycoplasma-infected cells, shown in autoradiograms by the density of the grains and their distribution. Results obtained by the autoradiographic technique correspond approximately to specific activity values of RNA-infected cells after the incorporation of [3H]uridine and [3H]uracil.

Changes in cell-surface glycosaminoglycans in human diploid fibroblasts during in vitro aging

Changes in glycosaminoglycans during in vitro aging were investigated in human diploid fibroblasts. The cells were found to produce predominantly hyaluronate and smaller amounts of chondroitin 4-sulfate, chondroitin 6-sulfate, dermatan sulfate and heparan sulfate. Accumulation of heparan sulfate on the cell surface was notable during aging. Total glycosaminoglycan production in preconfluent culture did not change with population doubling level (PDL), while in confluent culture a decline in glycosaminoglycan production was observed. In contrast with this, heparan sulfate on the cell surface increased as a function of PDL in both confluent and preconfluent cultures. The distribution pattern of heparan sulfate in medium and cell surface indicated that the increase in heparan sulfate on the cell surface could be attributed to an increased accumulation on the cell surface, but not to an elevated production. Thus, we conclude that the increased accumulation of heparan sulfate on the cell surface might be involved in an age-related alteration in the cell membrane.

Facilitated transport of uracil and 5-fluorouracil, and permeation of orotic acid into cultured mammalian cells

The mode of permeation of uracil, 5-fluorouracil, and orotic acid into cells has been investigated in four established cell lines (Novikoff rat hepatopma, P388 mouse leukemia, mouse L., and Chinese hamster ovary cells) in attempts to assess the rate-determining step(s) in their incorporation into the nucleotide pool and nucleic acids. Uracil and 5-fluorouracil shared a saturable transport system (Km = 5 to 15 mM) capable of rapid equilibration of these substrates across the cell membrane (t 1/2 at 25 degrees in first-order range of concentration = 25 to 58 sec). Thus it seems unlikely that transport is limiting the incorporation of uracil or fluorouracil. Their transport was inhibited by various nucleosides and hypoxanthine. Only the non-ionized form of fluorouracil was a substrate for the transporter; exclusion of charged pyrimidines may explain why orotate was not a substrate at physiological pH. Orotate permeated the cell membrane much more slowly (t 1/2 = 2890 to 6930 sec); its permeation was apparently non-mediated and rate-determining in the conversion of extracellular orotate to intracellular nucleotides.

Macrophages overcome mycoplasma infections of cells in vitro

Mycoplasmal infections still cause severe problems in cell cultures, particularly permanent lines, and although rapid detection is possible the only methods proposed for the elimination of the mycoplasma are either laborious or unsatisfactory. Treatment with antibiotics often leads to the development of resistance and we have found it more successful to passage contaminated cells in nude (thymusless) mice although the cells cannot always be recovered. But when the resulting subcutanous tumours can be collected, the cells are both free of mycoplasma and accompanied by a large number of macrophages. Because nude mice have no T cell-dependent immune response, it seemed possible that the macrophages could be responsible for the elimination of the mycoplasma. The experiments reported here support this hypothesis, and have led to a rapid and reproducible technique for eliminating mycoplasma in vitro by a brief co-cultivation of contaminated cells with mouse macrophages, in the presence of antibiotics.

Mycoplasmal infection of lymphocyte cell cultures: infection with M. salivarium

Many conclusions concerning cell culture mycoplasmas are based on data from studies in fibroblast cultures. Some conclusions may not be valid in other types of differentiated cell cultures. M. salivarium was isolated from 35 human lymphocyte cultures (HLC), 34 from the same laboratory. The organism grew to more than 10(8) colony forming units (CFU) per ml of lymphocyte suspensions and was readily detectable by microbiological culture, uridine phosphorylase, and uridine/uracil assays. Direct mycoplasmal assays on HLC by DNA fluorochrome staining and scanning electron microscopy (SEM) yielded artifacts that interfered with diagnosis. For DNA and SEM of HLC, inoculation into indicator cell cultures is recommended. M. salivarium infection of HLC did not produce any immediate difference in growth rates; however, infected cultures eventually died 14 to 29 passages after infection in contrast to uninfected controls. The same organism in 3T6 fibroblasts effected a 60% decrease in growth rate. Although M. salivarium is a frequent isolate from the oral cavity, it is a rare cell culture isolate. M. salivarium was able to initiate growth over a wide pH range, grew as well in cell cultures as in cell-free media, and was resistant to 50 microgram per ml of gentamycin, tylocine, kanamycin, and erythromycin. By Cot1/2 analysis, M. salivarium had a genomic molecular weight of 4.2 X 10(6) daltons. M. salivarium did not increase chromosome aberrations in one HLC. Some of these results have application to infection of HLC by other mycoplasmal species.