Abstract
This report describes a combined immunofluorescence and fluorescence viability stain applied as one staining solution for rapid detection of live Legionella pneumophila in mixed bacterial populations. Instead of sequential viability staining with the Invitrogen BacLight LIVE/DEAD staining kit followed by antibody-Alexa Fluor (AF) 647 conjugate staining to identify live L. pneumophila, a combined single cocktail solution staining protocol was developed to simplify and accelerate the time to detection of viable L. pneumophila serogroup-1 (SG-1) in mixed species populations on a filter membrane. The stain cocktail will aid in accelerating fluorescence microscopic analysis of cooling tower, air conditioner and water fountain or other liquid samples for the presence of L. pneumophila and its viability status. Visibly red stained cells were identified as dead non-L. pneumophila SG-1 cells, while green fluorescing cells represented viable non-L. pneumophila SG-1 cells. Due to also staining red with antibody-AF 647, L. pneumophila SG-1 cells were pseudocolorized as blue to distinguish them from other dead cells. Fluorescence color emission mixing from the viability dyes (SYTO 9 and propidium iodide) with antibody-AF 647 stained L. pneumophila led to other fluorescent colors. For example, green plus pseudocolorized blue AF 647-antibody- labeled cells were identified as live cyan-colored L. pneumophila SG-1 cells. Magenta-colored cells resulted from dead L. pneumophila cells that combined red propidium iodide with blue pseudocolorized AF 647-antibody emissions. Analysis of measured RGB (red, green, blue) color values in microscopic images of mixed bacterial populations suggests the possibility of facile automated discrimination of subpopulations of live and dead L. pneumophila and non-L. pneumophila species by computers in 3-dimensional RGB color space after staining in the combined cocktail which will save time for more rapid microscopic detection of potential sources of Legionnaire’s disease.
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All data generated or analyzed during this study are included in this published article and the supplemental data file.
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The authors can make custom code related to movement of the microscope stage, automated recognition, counting, outlining and RGB color image analysis of bacterial cells available to interested parties.
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Work was funded by a Center for Disease Control (CDC) SBIR contract no. 75D30120P09235.
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JGB conceived the overall experiments and wrote the manuscript, JJJ designed and conducted all bacterial fluorescence viability and immunofluorescence staining experiments and CJM provided assistance with microscopic image acquisition, RGB image stacking, automated bacterial recognition, counting and image analysis. All three authors edited the manuscript.
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John, J.J., May, C.J. & Bruno, J.G. A Combined Immunofluorescence and Fluorescent Viability Cocktail Staining Procedure for Rapid Microscopic Detection and Enumeration of Live Legionella pneumophila. J Fluoresc 31, 1425–1432 (2021). https://doi.org/10.1007/s10895-021-02776-3
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DOI: https://doi.org/10.1007/s10895-021-02776-3