Preliminary Isolation and Antibacterial Activity of the Ethyl Acetate Extract of Prinsepia utilis Royle in Vitro

Seven fractions were isolated from the ethyl acetate extract of Prinsepia utilis Royle by silica gel column chromatography. The antibacterial activities determined by disc diffusion method in vitro, indicated that the first and fourth fractions showed better antibacterial activity than the other fractions, while the sixth and seventh fractions did not showed any antibacterial activity. The diameters of the inhibition zone of first and fourth fractions were greater than 10 mm against three standard strains (Staphylococcus aureus ATCC25923, Escherichia coli ATCC44102 and Salmonella sp. CMCC(B)50041) at the concentration of 20 mg/ml. The first fraction was then repeatedly recrystallized in acetone to yield a white snowflake-like compound A, the inhibition zones of which were 14.03 mm, 11.54 mm and 12 mm, respectively. The Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) were measured by broth dilution method at the concentrations ranging from 20 to 0.313 mg/mL. The MIC and MBC values of the first, fourth fractions and compound A were lower than that of oregano oil (positive control) against S. aureus ATCC25923.