Use of image-based flow cytometry in bacterial viability analysis using fluorescent probes.

This protocol was developed to utilize imaging flow cytometry (IFCM) in combination with fluorescent dyes to both enumerate and analyze morphological features of live and dead cells in a mixed live/dead bacterial sample. The fluorescent dyes used in this protocol include 5(6)-carboxyfluorescein diacetate (CFDA), which indicates the functional activity of esterase inside viable bacterial cells, and DRAQ7, a dye that exploits membrane-compromised bacterial cells to enter and stain the cell. The live cell population stained with CFDA emits a fluorescent green color while the dead cell population stained with DRAQ7 emits a fluorescent red color, which allows the two populations to be distinctively separated by the IFCM system. Additionally, the cytometer captures a clear image of each object, which can then be analyzed for morphology features. The IFCM system is able to reliably, accurately, and precisely determine a bacterial cell concentration as long as the concentration of cells in a sample is no less than 1 × 10(3) cells/ml. The two dyes, CFDA and DRAQ7, have been demonstrated to be an effective stain combination for bacterial viability analysis.