Fluorescence assessment of Lactococcus lactis viability

The reproduction and activity of lactic acid bacteria (LAB) are essential i n their applications in the dairy industry and other fermentations. Traditi onally used methods like plate counting and acidification tests require lon g incubation times and provide limited information. Fluorescence techniques provide possibilities for rapid assessment of cell physiology. We used tra ditional and fluorescence assays to assess the physiological condition of L . lactis subsp. lactis ML3 cultures that were exposed to various stress con ditions. After exposure to some of the stress conditions, carboxyfluorescei n (cF) labelling did not agree with plate counts. Therefore, a two-step met hod was developed in which cF labelling was followed by a lactose-energized efflux assay. The combined assay proved to be a good and rapid indicator f or reproduction and acidification capacity of stressed L. lactis. This nove l assay has potential for physiological research and dairy applications rel ated to LAB. (C) 2000 Elsevier Science B.V. All rights reserved.