MIC determination
The resistance of bacteria to the antibiotics and the minimum
inhibitory concentration (MIC) of natural antimicrobials were
determined by standard broth microdilution (Wiegand, Hilpert, &
Hancock, 2008). Beef-extract peptone medium was used for the
food-borne bacteria. Active cultures were generated by inoculating
the thawed microbial stock suspensions into nutrient broth followed
by overnight incubation at 37 C with shaking. The inoculums
were adjusted to final concentrations of 1 105 cfu/mL by
comparison with a McFarland No. 1 turbidity standard. The natural
antimicrobials were dissolved in beef-extract peptone medium
with DMSO in two-fold serial dilutions from 5 mg/mL to 0.078 mg/
mL. Then, 100 ml of the individual antimicrobials and 100 ml of the
1 105 cfu/mL bacteria were dispensed into the 96 well plates.