3.5. Minimum Inhibitory Concentration (MIC) Determination

MIC values were determined by the microdilution broth method using a final concentration of 5 × 105 CFU/mL. Seven strains of bacteria from ATCC (Medibac, Quito, Ecuador), three gram positive and four gram-negative bacteria were used for the assay. MIC was defined as the lowest concentration of substance that prevents visible growth of the organism in the microdilution wells (CLSI, M7-A7 2006). DMSO solutions of the samples were prepared at a concentration of 20 μg/mL for extracts and 200 μL/mL for essential oils. The assays were carried-out in 96-well plates (Eppendorf AG, Hamburg, Germany) and two-fold serial dilution was employed, to obtain decreasing concentrations of 1000–7.81 μg/mL (extracts) and 10,000–70.81 μg/mL. Incubation was at 37 °C for 24 h [48]. Gentamicin was used a positive control with a MIC value of 0.40 μg/mL except for E. faecalis where tetracycline was used (MIC 1.95 μg/mL).