Automated immunofluorescent speciation of oral bacteria using flow cytometry

Direct flow cytometry of anaerobic bacteria in human feces

We describe a flow cytometry method for analysis of noncultured anaerobic bacteria present in human fecal suspensions. Nonbacterial fecal compounds, bacterial fragments, and large aggregates could be discriminated from bacteria by staining with propidium iodide (PI) and setting a discriminator on PI fluorescence and by exclusion of events with large forward scatter. Since anaerobic bacteria, which account for over 99.9% of all fecal bacteria, die during sample preparation, a fixation step was not necessary. A second aim of this study was to investigate the technical possibility of measurement of in vivo IgA coating of fecal anaerobic bacteria as well as their bacterial size. Fecal samples of 22 healthy human volunteers were analyzed. The fluorescence distribution of IgA-coated bacteria labeled with fluorescein isothiocyanate (FITC)-anti-Hu-IgA had overlap with noncoated bacteria. However, with match region subtraction, detection of low levels of specific FITC fluorescence on IgA-coated bacteria was achieved. The median bacterial two-dimensional surface area was 1.0 microns2. To validate flow cytometry data, all samples were analyzed with an image analysis system as well. With this new method, a rapid evaluation of fecal flora with high sensitivity for specific FITC fluorescence is possible without culturing.

Flow-cytometric identification and detection of Porphyromonas gingivalis by a LPS specific monoclonal antibody

The purpose of this study was to identify Porphyromonas gingivalis (P. gingivalis) by flow cytometry (FCM) using a monoclonal antibody (MAb) OMR-Bg1E directed to P. gingivalis-specific lipopolysaccharide (LPS). The P. gingivalis strains ATCC 33277, 381, ESO75, W50, and A7A1 were selected for the study. Fusobacterium nucleatum (F. nucleatum), Prevotella intermedia (P. intermedia), Campylobacter rectus (C. rectus), Streptococcus sanguis (S. sanguis) and Actinobacillus actinomycetemcomitans (A. actinomycetemcomitans) served as controls. A suspension of 10(7) bacteria/ml of each bacteria was prepared and then reacted with a P. gingivalis specific MAb OMR-Bg1E and fluorescein isothiocyanate (FITC) labeled second antibody. These samples were analyzed by FCM. Bacterial specific binding aggregate on data was separated out by the forward- and side-angle-scatter characteristics, while non-specific binding (NSB) was eliminated by excluding the region with mouse IgG-positive and second antibody-positive area. FCM detected a mean range of 56.2% to 97.2% P. gingivalis strains. There was a 5.1% non-specific binding using FCM to non-P. gingivalis strains. When the P. gingivalis concentration was adjusted to 10(2), 10(4), and 10(6) bacteria/ml, a detection rate of 35.7%, 48.1%, and 91.4%, was respectively observed. The lower sensitivity of the flow cytometric assay was 10(2) bacteria/ml. When P. gingivalis was added to P. intermedia suspension at 1, 20, 40, 60, and 80%, the MAb-positive fraction yielded by FCM displayed a coefficient of determination of 0.967 with the actual percentage of P. gingivalis and could be regressed to a linear function.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of bacteria by multiparameter flow cytometry

An arc-lamp based flow cytometer was used to obtain high resolution measurements of the light scattering characteristics and DNA contents of eight different bacteria. Light scatter profiles of bacteria are a useful first step when flow cytometry is used to characterize organisms. Scanning and transmission electron microscopy of the bacterial samples demonstrate that the structural basis of the light scattering profiles is not always clear, i.e. some organisms appear to have anomalous light scattering characteristics. The use of a third measurement parameter, DNA content, allowed much better discrimination of the organisms. Flow cytometry shows great promise as a method for the rapid discrimination and identification of bacterial populations.

Limit of resolution of flow cytometry for the detection of selected bacterial species

The enumeration of bacteria in dental plaque samples is a vital but time-consuming procedure that uses standard cultural methods. Flow cytometry has proven to be a useful tool for the analysis of eukaryotic cells. In the present investigation, the utility of this technology for the enumeration of bacteria in mixtures was explored. Rabbit antisera were produced against the putative periodontal pathogens A. actinomycetemcomitans, B. intermedius, B. gingivalis, E. corrodens, W. recta, B. forsythus, as well as the frequently isolated supragingival species S. sanguis. Cross-reactive antibodies were removed by absorption, and the specificity of each antiserum was confirmed by being tested against a panel of 235 oral microbial strains (79 genera; 94 species) by means of ELISA. Conditions were established for the indirect immunofluorescent labeling of cells without agglutination with use of a goat anti-rabbit Ig-FITC second antibody. When an internal bead standard was used, it was found that unstained bacteria were enumerated by light-scattering parameters with poor efficiency (less than 3%). However, cells exposed to FITC either in the presence of specific or non-specific first antibody were enumerated with high efficiency (102.6 +/- 29.3%), indicating that a small amount of non-specific binding of fluorochrome facilitates bacterial detection. Clear discrimination between specifically- and non-specifically-stained bacteria was achieved with all six rabbit antisera. Mixtures of known composition were made (1) with pure cultures or (2) with a known species and supragingival plaque devoid of that species by culture. The results from both approaches with various species combinations revealed that the limit of resolution for accurate quantitation of a selected species was approximately 5%, although specific organisms could be detected qualitatively when present at approximately 1%.

Validation of flow cytometry for rapid enumeration of bacterial concentrations in pure cultures

Flow cytometry was investigated as a rapid detection and counting method for bacteria in pure cultures. A simple two-parameter detection scheme was employed: particle size was measured by forward angle light scatter and nucleic acid content by fluorescence of the DNA/RNA-binding dye ethidium bromide. The technique gave results that correlated exceptionally well with conventional plate counting for four species of bacteria, and concentrations in the range 10(2) to 10(7) cfu/ml. Cytometric counts were obtained in a few minutes, as compared with 2 d required for the plate counts. Under ideal conditions, each bacterial species examined exhibited a characteristic 'signature' on the cytometer, which could be explained by its known properties and morphology.

224Ra-induced osteopenia in male CBA mice

Six groups of young adult, male mice were injected with six dose levels of the bone-seeking, alpha-emitting radionuclide 224Ra (half-life 3.6 days); a seventh group was injected with saline alone. The administered doses were relatively low, ranging from 2 to 64 kBq per animal. The mice were maintained under standard laboratory conditions until they either died or became moribund, when they were killed. The mean ages at death of the experimental groups were not significantly different from the normal control group. Individual bones--the mandible, parietal, nasal, and bulla--were isolated and standard linear measurements and dry weights were obtained. In all measurements considered, the highest two administered amounts (32 and 64 kBq) caused a significant reduction relative to controls. Low power microscopy of the mandible revealed osteonecrosis in the high dose groups. This is similar to the condition of "radium jaw" which has been described as a late effect of either accidental ingestion or therapeutic administration of 226Ra (half-life 1,620 years) in man; the other bones did not show obvious osteonecrosis. This work emphasizes the long-term osteopenic effects of low-dose radium, even in the short-lived species 224Ra. It also provides a method of quantifying the osteopenic effect of bone-seeking radionuclides.

Flow cytometric identification of microorganisms by dual staining with FITC and PI

The identification of microorganisms by flow cytometry was evaluated by using a double staining technique with propidium iodide and fluorescein isothiocyanate and a two dimensional analysis. A diverse group of 19 different species and strains of microorganisms was tested to determine if they could be differentiated by flow cytometry. The organisms tested displayed characteristic and distinct two dimensional fluorescent patterns which allowed ready grouping and differentiation into subsets of organisms. The slopes and correlation coefficients of the histograms and the ratio of red to green signals expressed these differences quantitatively and allowed organisms to be placed into one of three groups based on these values. In some instances, as with Streptococcus pneumoniae and pyogenes and Staphylococcus aureus and epidermidis, it was possible to distinguish between species of bacteria from the same genus. The use of dual dye labeling and flow cytometry provided a rapid method of identifying selected microorganisms and may be broadly applicable for the detection and identification of many bacteria and fungi.

Flow cytometric screening and isolation of Escherichia coli clones which express surface antigens of the oil-degrading microorganism Acinetobacter calcoaceticus RAG-1

Flow cytometry (FCM) in conjunction with immunocytochemical-labeling was used to analyze and screen a population of Escherichia coli clones containing a genomic library from the oil-degrading microorganism Acinetobacter calcoaceticus RAG-1 surface antigens. Reconstruction experiments using mixed populations indicated that RAG-1 cells could be clearly distinguished at a ratio of one RAG-1 cell to 500 Escherichia coli cells. Using this technique two clones, WM143 and WM191, were isolated and shown by restriction endonuclease cleavage and Southern hybridization to contain plasmids carrying inserts of RAG-1 DNA of 9.4 and 9.8 kb respectively.

Biochemical and microanalytical methods

Because of the small amounts of material available for study, investigations of plaque, caries lesions in enamel, and antibodies in saliva pose difficult challenges for investigators. Sophisticated biochemical and fluorescence techniques can now be used to investigate the microbial composition of plaque, thereby avoiding the need for tedious culturing techniques from single sites on tooth surfaces. A range of microchemical methodologies is available which greatly facilitates the analysis of plaque fluid, thereby enhancing our understanding of tooth-plaque interactions. The application of a range of novel physiochemical techniques should help to clarify our knowledge of the interactions involved in pellicle formation and elucidate the phenomena involved in the formation of the early caries lesion. A range of techniques is now available for the study of antibodies in saliva. These include ELISA, RIA, and solid-phase immunoassay. The application of these methodologies to the investigation of oral diseases should facilitate our understanding of the pathogenesis of dental maladies at the molecular level.