it is demonstrated as one of the most antibacterial EO components
(Hyldgaard et al., 2012). The lowest concentration of O. vulgare EO
(0.5% v/w) acted as bacteriostatic on DIL 1, DIL 2 and DIL 3 Listeria
populations; only after 11 days of preservation at 4 C, bacterial
concentration of DIL 4 (concentration higher than 40 CFU/g at T0)
reached 0 CFU/g (MBC). The 1% and 2% (v/w) concentration of O.
vulgare EO inhibited bacterial cells in time and bacterial concentration
dependent mode: Listeria concentration decreased continuously
reaching the lowest values at the end of the experiments (14
days of preservation at 4 C), and regression line slope coefficient absolute values had increasingly large values going from DIL 1 to
DIL 4 [respectively 0.17, 0.18, 0.29, 1.48 for 1% (v/w) and 0.37, 0.41,
0.56, 0.60 for 2% (v/w)], showing the increase of the EO action with
the decrease of the pathogen concentration and the increase of EO
concentration. Furthermore, only 1% and 2% concentrations (v/w)
of this EO were able to kill (MBC) all Listeria cells of DIL 4 (containing
more than 30 and 40 CFU/g respectively) at the second day
of preservation at 4 C, 2% (v/w) also being able to cause the
decrease of the Listeria load of DIL 3 (initial load of more than
590 CFU/g) till 0 CFU/g at the end of the experiment (MBC).
The three concentrations of Oregano (0.5%, 1% and 2% v/w)
reduced staphylococcal load in meat samples during their preservation
at 4 C in a time dependent mode, as did Thymus. Differently
from Thymus, Oregano had a dose dependent mode of inhibition,
2% (v/w) of the oil reducing the staphylococcal load more than the
1% (v/w), which had a greater bactericidal effect than 0.5% (v/w).
This is confirmed by the increase of the slope coefficient absolute
values of the regression lines from DIL 1 to DIL 4, in each EO concentration,
and between the three EO concentrations and by MIC
values (Table 8).