In this paper a staining procedure for detection of viable starter culture cells (Lactobacillus, Pediococcus) is described. The method is based on fluorescence in microscopy and staining with two fluorochromes, Erythrosine B (ERB) and 4′, 6-diamidino-2-phenylindole (DAPI). The staining procedure revealed viable cells by bright blue or bright green fluorescence, whereas dead or heat-treated cells had only low intensity fluorescence. Counting of viable cells of lactic acid bacteria dried on microscope slides was carried out both manually and by an image analyser, and was compared with the results from the conventional plating method and from adenosine 5-triphosphate (ATP) determinations. The bacterial cells were dried on microscope slides before staining to give an indication of whether the staining procedure may be useful for detection of viable and dead cells in cryosections. The staining pattern observed with Lactobacillus and Pediococcus cells was not confirmed with Micrococcus cells.
Karwoski, M., Venelampi, O., Linko, P., & Mattila-Sandholm, T. (1995). A staining procedure for viability assessment of starter culture cells. Food Microbiology, 12, 21-29. https://doi.org/10.1016/S0740-0020(95)80075-1