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Applied and Environmental Microbiology, May 2001, p. 2326-2335, Vol. 67, No. 5
Laboratory of Food Microbiology, Department
of Food Technology and Nutritional Sciences, Wageningen University
and Research Centre, 6700 EV Wageningen, The Netherlands
Received 21 July 2000/Accepted 10 November 2000
The viability of lactic acid bacteria is crucial for their
applications as dairy starters and as probiotics. We investigated the
usefulness of flow cytometry (FCM) for viability assessment of lactic
acid bacteria. The esterase substrate carboxyfluorescein diacetate
(cFDA) and the dye exclusion DNA binding probes propidium iodide (PI)
and TOTO-1 were tested for live/dead discrimination using a
Lactococcus, a Streptococcus, three
Lactobacillus, two Leuconostoc, an
Enterococcus, and a Pediococcus species. Plate count experiments were performed to validate the results of the FCM assays. The results showed that cFDA was an accurate stain for live
cells; in exponential-phase cultures almost all cells were labeled,
while 70°C heat-killed cultures were left unstained. PI did not give
clear live/dead discrimination for some of the species. TOTO-1,
on the other hand, gave clear discrimination between live and dead
cells. The combination of cFDA and TOTO-1 gave the best
results. Well-separated subpopulations of live and dead cells could be
detected with FCM. Cell sorting of the subpopulations and subsequent
plating on agar medium provided direct evidence that cFDA labels the
culturable subpopulation and that TOTO-1 labels the
nonculturable subpopulation. Applied to cultures exposed to
deconjugated bile salts or to acid, cFDA and TOTO-1 proved to
be accurate indicators of culturability. Our experiments with lactic
acid bacteria demonstrated that the combination of cFDA and
TOTO-1 makes an excellent live/dead assay with versatile applications.
0099-2240/01/$04.00+0 DOI: 10.1128/AEM.67.5.2326-2335.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Flow Cytometric Assessment of Viability of Lactic Acid
Bacteria
*
Corresponding author. Mailing address: Laboratory of
Food Microbiology, Department of Food Technology and Nutritional
Sciences, Wageningen University and Research Centre, P.O. Box 8129, 6700 EV Wageningen, The Netherlands. Phone: 31 317 484981. Fax: 31 317 484893. E-mail:
Tjakko.Abee{at}micro.fdsci.wag-ur.nl.
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