Agar-well diffusion: The assay was conducted as described by
Perez et al. (1990). Briefly, microorganisms from growth on nutrient
agar incubated at 37°C for 18 h were suspended in saline solution
0.85% NaCl and adjusted to a turbidity of 0.5 Mac Farland
standards (108 cfu/ml). The suspension was used to inoculate 90
mm diameter Petri plates with a sterile non toxic cotton swab on a
wooden applicator. Six millimeters diameter wells were punched in
the agar and filled with 50 μl of 2000 μg/ml alkaloids. The
dissolution of the alkaloids was aided by 1% (v/v) DMSO which did
not affect microorganisms growth, according to our control
experiments. Commercial antibiotics were used as positive
reference standard to determine the sensitivity of the strains. Discs
were directly placed onto the bacterial culture. Plates were
incubated in air at 37°C for 24 h. Antibacterial activities were
evaluated by measuring inhibition zone diameters. The experiments
were conducted twice.