Endogenous HPRT activity in mycoplasmas isolated from cell cultures

Development and application of monoclonal antibodies for the detection of cell infecting mycoplasmas

Two hybridoma cell lines producing monoclonal antibodies (MAbs) to mycoplasmas were established by fusion of mouse myeloma and spleen cells obtained from mice immunized with whole cell Mycoplasma pneumoniae antigens. The MAbs designated as MYC-4 and MYC-9 bound to a single M. pneumoniae protein band with approximate molecular weights of 150,000. In dot-EIA both MAbs reacted with ten Mycoplasma spp., two serovars of Ureaplasma urealyticum and Acholeplasma laidlawii. The MAbs have great potential to be used as an antibody probe for the rapid screening of cell cultures and hybridomas for mycoplasmal contamination.

Alpha-5-phosphoribosyl-1-pyrophosphate-independent salvage of purines in cultured Chinese hamster lung fibroblasts

A variant clone of cultured chinese hamster lung fibroblasts (V79), selected for resistance to 8-azaguanine (V79 azagrst), although lacking hypoxanthine-guanine phosphoribosyltransferase (EC 2.4.2.8), is able to convert hypoxanthine into IMP via purine-nucleoside phosphorylase (EC 2.4.2.1) and nucleoside kinase. In addition to the phosphoribosylation pathway, we also present evidence for the occurrence of a kinase-mediated pathway of recovery of hypoxanthine in the wild-type cells. The lower rate of formation of IMP in the V79 azagrst cells, apparently correlated with the phosphorylation of the nucleoside, suggests possible differences in the catalytic and/or regulatory properties of nucleoside kinase in the two cell lines. This fact might be of particular relevance in evaluating the mechanisms of resistance to purine analogs displayed by several cell types.

Problems and pitfalls in assessing human T-lymphocyte mutant frequencies

The measurement of 6-thioguanine-resistant frequencies in human T-lymphocytes has been used to quantitate the in vivo HPRT mutant frequency. The data so far indicate a large variability in normal healthy individuals. The reliability with which wells are identified for clonal growth in the assay was investigated using 5 different methods of scoring: visual scoring, uptake of [3H]thymidine (either by cut off point or by statistical analysis), cell count and cytogenetic analysis. None of these methods presented a viable means of scoring the assay. An examination of the statistical precision of the assay under the limitations imposed by the experimental conditions leads to the conclusion that there is a large inherent error associated with the estimated mutant frequencies. Analysis of the T-lymphocyte subpopulations by cell surface monoclonal antibodies also leads us to believe that the observed mutant frequencies may not be representative of the true in vivo mutant frequencies. If the assay is to be used as a sensitive screen for individual or population exposure to possible mutagens, a closer understanding of the biology of the assay is indicated, and a comprehensive reevaluation of the methodology required. The utility of the system for studying qualitative aspects of human mutagenesis is not in doubt.

Influence of Mycoplasma arginini infection on the induction of aryl hydrocarbon hydroxylase by TCDD in rat hepatoma cell cultures

Mycoplasma arginini was eliminated from a rat hepatoma cell line (H-4-II-E) by plating at low cell density and treatment with chlortetracycline (250 micrograms/ml), kanamycin (250 micrograms/ml), tylosin (100 micrograms/ml), 3% M. arginini antiserum and 5% fresh guinea-pig serum. The induction of AHH activity in the cell culture was measured in response to increasing concentrations of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The ED50 values (estimated doses that produce 50% maximum enzyme induction) were calculated to be 0.256, 0.452 and 0.344 pmol TCDD/plate for original, mycoplasma-free and reinfected cells, respectively. Although the absence of M. arginini in the rat hepatoma cell line makes the cells slightly less responsive to AHH induction by TCDD, this decrease does not detract from the use of the method to screen food extracts and environmental samples for the presence of certain toxic planar organic compounds.

Enzymatic activities on purine pyrimidine metabolism in nine mycoplasma species contaminating cell cultures

The study of mycoplasma enzymes involved in nucleotide degradation and base salvage pathways allowed determination of enzyme profiles for some species. The activity of adenosine phosphorylase seems to be the biochemical test of choice to detect mycoplasma contamination in cell cultures. All mycoplasmas tested had a very high level of activity compared to very low activity in human cell cultures, rendering the technic sensitive even at a low degree of contamination.

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.

Factors influencing microbiological assay of cell-culture mycoplasma

A total of 6432 cell cultures was assayed for mycoplasmas over a 6-year period by aerobic and anaerobic incubation of agar and broth media. Mycoplasmas were detected in 375 cultures (5.8%). M. orale and A. laidlawii accounted for 61.3% of the isolates. Anaerobic incubation detected 98.1% of the isolates; aeorbic incubation detected 45.8%. Of factors studied to determine their effect on mycoplasma assay, only two, anaerobic incubation and presence of mycoplasmacidal/static antibiotics, were significant. In separate studies, 86 of 2656 cell cultures (3.2%) were infected with strains of M. hyorhinis that did not grow on cell-free media. Recommendations are given for microbiological assay of cell-culture mycoplasmas.