*2.3. Antimicrobial Activity*

Strains used for determining antimicrobial activity included *Bacillus subtilis* ATCC 6051, *B. alvei* ATCC 6344, *B. cereus* ATCC 21772, *B. megaterium* ATCC 25848, *B. pumilus* ATCC 7061, *Staphylococcus aureus* ATCC 6538, *S. epidermidis* ATCC 14990, *S. saprophyticus* ATCC 15305, *Enterococcus faecalis* ATCC 29212, *Mycobacterium smegmatis* ATCC 19420, *Escherichia coli* ATCC 9637, *Proteus mirabilis* CECT 170, (from Type Culture Spanish Collection), *Pseudomonas aeruginosa* AK 958 (from the University of British Columbia, Department of Microbiology collection), *Salmonella sp*. CECT 456, *Klebsiella oxytoca* LMM2 (clinical isolate, University of La Laguna), and *Candida albicans* CECT 1039. The bacteria cultures were developed in nutrient broth (NB) or brain heart infusion broth (for *E. faecalis* and *M. smegmatis* containing 0.06% Tween 80), and the yeas<sup>t</sup> was cultured in Sabouraud liquid medium at 37 ◦C. All culture media were purchased from Oxoid. The minimum inhibitory concentrations (MICs) were determined for each compound in triplicate by broth microdilution method (range 0.08–40 μg/mL) in 96 well microtitre plates, according to the M07-A9 of the CLSI (Clinical and Laboratory Institute) [32]. Wells with the same proportions of dimethyl sulfoxide (DMSO) were used as controls and never exceeded 1% (*v*/*v*). The starting microorganism concentration was approximately 1–5 × 10<sup>5</sup> CFU/mL, and growth was monitored by measuring the increase in optical density (OD) at 550 nm (OD550) with a microplate reader (Multiskan Plus II, Tritertek, Huntsville, AL, USA) and viable count in agar plates. The MIC was defined as the lowest concentration of compound that completely inhibits growth of the organisms compared with that of the control after incubation time.

#### **3. Results and Discussion**
