Antibacterial activity of the crude extracts and fractionated constituents of Myrtus communis

The antibacterial activity of methanol crude extract of Myrtus communis L. (Myriaceae) was evaluated against 10 laboratory strains of microorganisms, including 6 Gram positive (Staphylococcus aureus, Micrococcus luteus, Streptococcus pneumoniae,, Streptococcus pyogenes, Streptococcus agalactiae, Listeria monocytogenes) and 4 Gram negative bacteria (Escherichia coli,, Proteus vulgaris, Pseudomonas aeruginosa and Campylobacter jejuni). The crude extract inhibited the growth of all tested bacteria except C jejuni. The inhibition zone diameter for 0.5 mg/ml of the crude extract (fraction M) varies from 18 nun for S. aureus to 8 nun for S. agalactiae, and minimum inhibitory concentrations (MIC) range from 0.1 for S. aureus and M. luteus to over 2 mg/ml for E. coli. Further extraction of fraction M with diethyl ether, ethyl acetate, and ethanol results in 6 different fractions (M1-M6). These fractions were screened for antibacterial activity against the non-fastidious bacteria (S. aureus, M. luteus, E. coli, P vulgaris, and P aeruginosa). The diethyl ether extracted fraction (fraction M1) showed the highest level of activity in comparison to fraction M and other fractions. The MIC for S. aureus and M. luteus were reduced from 0.1 in the fraction M to 0.025 mg/ml in fraction M1 and for E. coli and P aeruginosa was reduced from over 1 mg/ml in fraction M to 0.1 mg/ml in fraction M1. Essential oil was also active against the tested bacteria, and M. luteus showed the highest level of sensitivity (NEC 1:1600). The presence of antibacterial activity in different fractions and essential oil indicates that the extract possesses different compounds, which have different activities.