ATIVIDADE ANTIMICROBIANA DE ÓLEOS ESSENCIAIS DE - UFSM

this suspension was inoculated in each well containing the essential oils. The microplates
were incubated for 24 hours at 35ºC under aerobic conditions. The MIC was defined as the
lowest concentration of essential oil resulting in the complete inhibition of bacterial growth.
These tests were performed in triplicate.
Determination of minimum bactericidal concentrations
The minimum bactericidal concentration (MBC) was defined as the lowest
concentration of essential oil that killed the inoculating microorganisms. The MBC was
determined by the absence of visible bacterial growth in wells after 24 hours of incubation.
From these wells, a 10 μl aliquot was inoculated on Mueller-Hinton agar. After 24 hours of
incubation at 35°C, the lowest concentration of essential oils that resulted in no bacterial
growth was recorded. These tests were performed in triplicate.
Statistical analysis
The nonparametric Mann-Whitney test was used to determine whether groups had
similar susceptibility patterns to a particular essential oil.
RESULTS
The isolates in this study showed variations in their sensitivity to different essential
oils. The geometric means for the MICs and MBCs against E. coli isolated from the feces and
viscera of swine were the following: O. vulgare (MIC = 1463.1 µg/ml; MBC = 1564.6
µg/ml), L. graveolens (MIC = 2392.8 µg/ml; MBC = 2675.9 µg/ml), T. vulgaris (MIC =
2736.4 µg/ml; MBC = 2736.4 µg/ml) and C. zeylanicum (MIC = 5004.5 µg/ml; MBC =
5723.0 µg/ml) (Table 1).
Subgroups of isolates with similar number of virulence factors (Table 2) showed
similar sensitivity (P>0.05) to corresponding concentrations of each essential oil. There was
no significant difference (P>0.05) between resistotype subgroups A and B (Table 3).
The geometric mean of the MICs indicated that oregano essential oil was the most active
(P