Flow cytometric analysis of Lactobacillus plantarum to monitor lag times, cell division and injury.

Flow cytometry in combination with fluorescent molecular markers 5- (and 6-) carboxyfluorescein succinimidylester (CFSE) and propidium iodide (PI) have been applied to determine lag times, numbers of cell divisions and injury after mild heat (50 degrees C, 5 min) and nisin treatments (0.1 and 1.0 microgram ml-1) of Lactobacillus plantarum. Initial labelling with covalently bound dye CFSE (20 and 100 micrograms ml-1) allowed determination of lag times and cell proliferation for up to eight generations. Double-labelling with CFSE and PI (5 micrograms ml-1) provided additional information about damage levels and distributions within populations. Subpopulations surviving treatment could be identified easily and selectively sorted.