3.5.2. JC-1 stained cells
The JC-1 staining of inoculated untreated microscopy samples
showed that almost all of the cells retained full membrane potential
as demonstrated by the strong red fluorescence (Fig. 3); a small
fraction of stained cells (a single cell in Fig. 3) exhibited different
levels of reduction in the membrane potential (yellow/green fluorescence)
in all of the examined fields, approximately reflecting the
variability of the working suspensions within the calculated
threshold value.
For JC-1 staining only E (Fig. 4) and D samples can be considered,
as for LIVE/DEAD BacLight. Also in this circumstance, the number of
injured cells from the plate counts does not differ dramatically from
that of the green/yellow JC-1 stained cells. Such a result may suggest
the hypothesis that the largest majority of sub-lethally injured
cells from the D and E treatments suffer an impaired membrane
potential and that green depolarized cells should be dead. Nonetheless,
in spite of the coarse numerical correspondence between
cells with partially depleted membrane potential and their inability
to grow on selective media, complete information on the actual
physiological state of injured cells is not given.
Moreover, JC-1 staining revealed a population with a very
different reduction rate of the membrane potential; on the basis of
visual assessment of colour intensity and red-yellow/green fluorescence
shift, cells showed a range of intermediate membrane
potential between untreated or thermally inactivated cells, and
such a non-homogenous distribution of membrane depolarization
among cells was also detected in a fraction of the bufferpressurized
L. monocytogenes population by Ritz et al. (2001).