3.1.2. Inhibition halo test for gallic acid
Bacteria were cultured for 24 h on LB agar plates with a series of
wells containing different amounts of gallic acid. As shown in Fig. 2,
the diameters of the growth inhibition zones around the wells
increased gradually with the content of gallic acid in the range from
0 for the control condition to 12 mm for the presence of 2.5 mg of
gallic acid. Growth inhibition halos were significantly higher than
control (p < 0.05) with amounts of gallic acid equal or greater than
1.0 mg.
3.1.3. Kinetics of bacterial growth inhibition by gallic acid
E. coli in LB mediumwas exposed to 4.5 mg/mL of gallic acid and
incubated for various lengths of time ranging from 0 to 360 min.
After incubation, aliquots of the cell suspension were evenly seeded
on LB agar to determine the CFU/mL value. As shown in Fig. 3, the
CFU/mL values decreased continuously from 3 108 to 8 103 with
the time of exposure to gallic acid in a range of 360 min. Decrease in
E. coli viability became statistically significant (p < 0.05) after
60 min of incubation. At 180 min of exposure to gallic acid growth
inhibition was 99.9%.