Shigella flexneri

Antibacterial activity was measured by modifying the method of Brandt et al. (19 (link)). E. coli (KCTC 1682), Vibrio paraheamolyticus (KCTC 2729), Pseudomonas aeruginosa (KCTC 1750), Shigella sonnei (KCTC 2518), and Shigella flexneri (KCTC 22192) were purchased from the Korean Collection for Type Cultures (Daejeon, Korea). All samples (10 mg/mL) were dissolved in 50 mM potassium phosphate buffer (pH 7.0) and filtered through a sterilized 0.2 μm syringe filter (Millipore, Temecula, CA, USA). The bacterial cells were incubated in brain heart infusion broth (Oxoid Ltd., Basingstoke, England) for E. coli, P. aeruginosa, S. sonnei, and S. flexneri, and tryptic soy broth (17 g/L of pancreatic digest of casein, 3 g/L of papaic digest of soybean, 2.5 g/L of dextrose, 5 g/L of sodium chloride, and 2.5 g/L of dipotassium phosphate) with 3% NaCl for V. parahaemolyticus at 37°C for 16 h, diluted with 200 μL of a liquid medium inoculated at about 10⁶ CFU/mL, and 100 μL of the samples were mixed with the bacteria in 96-well plates. Sterilized liquid medium (100 μL) was used as a control, and samples were cultured at 37°C for 24 h. Using a microplate reader, the absorbance values were compared at 600 nm during the incubation period, and data is expressed as growth inhibition rate (%).