Involvement of RNA and DNA in the staining of Escherichia coli by SYTO 13

SYTO-13, a Viability Marker as a New Tool to Monitor In Vitro Pharmacodynamic Parameters of Anti-Pneumocystis Drugs

While Pneumocystis pneumonia (PcP) still impacts the AIDS patients, it has a growing importance in immunosuppressed HIV-negative patients. To determine the anti-Pneumocystis therapeutic efficacy of new compounds, animal and in vitro models have been developed. Indeed, well-designed mouse or rat experimental models of pneumocystosis can be used to describe the in vivo anti-Pneumocystis activity of new drugs. In vitro models, which enable the screening of a large panel of new molecules, have been developed using axenic cultures or co-culture with feeder cells; but no universally accepted standard method is currently available to evaluate anti-Pneumocystis molecules in vitro. Thus, we chose to explore the use of the SYTO-13 dye, as a new indicator of Pneumocystis viability. In the present work, we established the experimental conditions to define the in vitro pharmacodynamic parameters (EC50, Emax) of marketed compounds (trimethoprim/sulfamethoxazole, pentamidine, atovaquone) in order to specifically measure the intrinsic activity of these anti-P. carinii molecules using the SYTO-13 dye for the first time. Co-labelling the fungal organisms with anti-P. carinii specific antibodies enabled the measurement of viability of Pneumocystis organisms while excluding host debris from the analysis. Moreover, contrary to microscopic observation, large numbers of fungal cells can be analyzed by flow cytometry, thus increasing statistical significance and avoiding misreading during fastidious quantitation of stained organisms. In conclusion, the SYTO-13 dye allowed us to show a reproducible dose/effect relationship for the tested anti-Pneumocystis drugs.

Multianalyte microphysiometry reveals changes in cellular bioenergetics upon exposure to fluorescent dyes

Fluorescent dyes have been designed for internal cellular component specificity and have been used extensively in the scientific community as a means to monitor cell growth, location, morphology, and viability. However, it is possible that the introduction of these dyes influences the basal function of the cell and, in turn, the results of these studies. Electrochemistry provides a noninvasive method for probing the unintended cellular affects of these dyes. The multianalyte microphysiometer (MAMP) is capable of simultaneous electrochemical measurement of extracellular metabolites in real-time. In this study, analytes central to cellular metabolism, glucose, lactate, oxygen, as well as extracellular acidification were monitored to determine the immediate metabolic effects of nuclear stains, including SYTO, DAPI dilactate, Hoechst 33342, and FITC dyes upon the pheochromocytoma PC-12 cells and RAW 264.7 macrophages. The experimental results revealed that the SYTO dye 13 significantly decreased glucose and oxygen consumption and increased extracellular acidification and lactate production in both cell lines, indicating a shift to anaerobic respiration. No other dyes caused significantly definitive changes in cellular metabolism upon exposure. This study shows that fluorescent dyes can have unintended effects on cellular metabolism and care should be taken when using these probes to investigate cellular function and morphology.

Use of SYTO 13, a fluorescent dye binding nucleic acids, for the detection of microparticles in in vitro systems

Microparticles (MPs) are small membrane-bound vesicles that are released from activated or dying cells by a blebbing process. These particles contain nuclear and cytoplasmic components and represent unique biomarkers for disease. The small size of particles, however, limits detection using flow cytometry with either light scatter or staining for surface markers. Because MPs contain DNA and RNA, we have explored the use of SYTO 13, a member of the class of SYTO dyes, for particle detection. SYTO 13 is cell permeable and has a high fluorescent yield when bound to DNA or RNA. In this study, we compared detection of MPs using either light scatter or SYTO 13 staining, testing the hypothesis that, with fluorescence detection with SYTO 13, problems of "noise" with light scatter are reduced and the range of MP sizes detected is increased. In these experiments, particles were obtained from lymphoid cell lines treated in vitro to undergo apoptosis. As these results showed, STYO 13 allowed the detection of 1.5-2.9 times as many particles as did light scatter. The increased sensitivity was observed with three different cell lines and was independent of inducing stimulus. Treatment of fixed and permeabilized MPs with DNase and RNase showed that SYTO 13 binding resulted from interaction with both DNA and RNA. Together, these findings indicate that the nucleic acid content of MPs provides the basis for their detection in in vitro systems and suggests the utility of fluorescent dyes like SYTO 13 for more sensitive quantitative assays.

A comparative study of the cytometric characteristics of high and low nucleic-acid bacterioplankton cells from different aquatic ecosystems

Flow cytometry has revealed the existence of two distinct fractions of bacterioplankton cells, characterized by high and low nucleic acid contents (HNA and LNA cells). Although these fractions seem ubiquitous in aquatic systems, little is known concerning the variation in the cytometric parameters used to characterize them. We have performed cytometric analyses of samples from a wide range of aquatic systems to determine the magnitude and variability in the cytometric characteristics of HNA/LNA. We show that neither group is associated to a fixed level of fluorescence and of light scatter. Rather, the relative position of HNA and LNA in the fluorescence versus side scatter cytograms varies greatly, both within and among ecosystems. Although the cytometric parameters of both groups tend to covary, there is often uncoupling between the two, particularly in light scatter. Our results show that, although the basic HNA/LNA configuration is present in most samples, its cytometric expression changes greatly in different ecosystems and along productivity gradients. The patterns in cytometric parameters do not support the simple, dichotomous view of HNA and LNA as active and inactive cells, or the notion of two distinct and independent communities, but rather suggest that there may be cells that are intrinsic to each fraction, as well as others that may exchange between fractions.

Rapid G+ count and subpopulation assessment of the intestinal bacteria in Apodemus sylvaticus and Mus musculus by flow cytometry

We report a novel application of calcein-acetomethyl ester in flow cytometry for rapid estimation of the number of G+-bacteria in rodent feces (Apodemus sylvaticus and Mus sp.f. muridae). We also use the combined application of flow cytometry and Syto-13 or Sypro Orange staining to count rapidly the total bacterial population and to describe bacterial subpopulations in the intestine.

Statistical analysis and biological interpretation of the flow cytometric heterogeneity observed in bacterial axenic cultures

Histogram comparison and meaningful statistics in flow cytometry is probably the most widely encountered mathematical problem in flow cytometry. Ideally, a test for determining the statistical equality or difference of flow cytometric distributions will identify the significant differences or similarities of the obtained histograms. This situation is of particular interest when flow cytometry is used to study the heterogeneity of axenic bacterial populations. We have statistically measured the heterogeneity of successive cytometric measures, the modifications produced after 20 transfers from the same culture, and the differences between 20 subcultures of identical origin. The heterogeneity of the bacterial populations and the similarity of the obtained 360 histograms were analysed by standard statistical methods. We have studied bacterial axenic cultures in order to detect, quantify and interpret their cytometric heterogeneity, and to assess intrinsic differences and differences produced by laboratory manipulations. We concluded that the standard axenic cultures have a considerable intrinsic cellular and molecular heterogeneity. We suggest that the heterogeneity we have detected basically has two origins: cell size diversity and cell cycle variations.