FIG. 2.

Flow cytometric analysis of a genetically and metabolically complex cell mixture. This figure illustrates the power of single-cell staining methods in combination with flow cytometric analysis for the fluorescent “dissection” of complex microbial populations. Here, Salmonella enterica serotype Typhimurium is differentiated from a mixture of E. coli, Citrobacter freundii, Proteus vulgaris, and Shigella dysenteriae on the basis of both cytochemical activity (CTC staining) and genetic identity (Salmonella-specific FISH staining). A complex mixture containing both live and formalin-killed representatives of each cell type was incubated with CTC, fixed with 10% buffered formalin, hybridized with a Salmonella-specific DNA probe (Sal3-Cy5), and examined by flow cytometry. Four distinct populations can be seen. Clockwise from the bottom left, they are dead non-Salmonella members of the Enterobacteriaceae (A), live non-Salmonella members of the Enterobacteriaceae (B), live Salmonella (C), and dead Salmonella (D). The numbers in each quadrant represent percentages of the total population. The photographic inset provides a visual interpretation of the cytometry data. Reprinted from reference 209a with permission from the publisher.