Membrane potential (MP) was chosen as another aspect to
illustrate the mechanism of antibacterial action as it plays an
important role in bacterial physiology. MP is measured as the
difference in electric potential between the interior and the
exterior of a biological cell. MP as an element of the proton motive
force, it is involved in the generation of ATP (Mitchell, 1966). MP
alterations of bacteria can affect cell metabolic activity. A MP of
normal bacteria is generated by differences in the concentrations
of ions on opposite sides of the cell membrane. Any treatments
depolarize the cellmembrane are deemed to reduce the volume of MP. Novo, Perlmutter, Hunt, and Shapiro (1999) stated that
carbonyl cyanidem-chlorophenylhydrazone could reduce bacteria
MP to zero or near zero while the other group (Rodriguez, Seguer,
Rocabayera & Manresa, 2004) reported the disturbance in
S. aureus MP and structural changes caused by three surfactants.
For this study, the fluorescence intensity is directly correlated
with the bacteria MP. Our results showed that the mean fluorescence
intensity of R123 reduced obviously after addition of cinnamon
EO. The loss of fluorescence indicates cell membrane
depolarization leading to irregular cell metabolic activity and
bacteria death.