Antibacterial activity of five oil bearing Ethiopian medicinal plants against eleven pathogenic bacterial strains

The antibacterial activity of volatile fractions from Artemesia abyssinthium, Croton macrostachyus, Echinops kebericho and Satureja punctata has been tested against selected Gram-positive and Gram-negative bacterial strains. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of five essential oils were investigated for their antibacterial activities against four gram-positive (Staphylococcus aureus (ATCC 25923), Streptococcus pyogenes, Listeria monocytogenes and Bacillus cereus) and seven gram-negative (Escherichia coli (ATCC 25922), Pseudomonas aeruginosa (ATCC 27853), Salmonella paratyphi, Shigella dysenteriae, Citrobacter sp., Klebsiella pneumonia and Proteus mirabilis) bacterial species. All the essential oils were active against all tested bacterial species. L. monocytogenes, B. cereus, and S. aureus were the three most sensitive bacteria with a mean concentration of 0.14, 0.8 and 0.62µg/ml, respectively. Almost all the essential oils have shown least activities against L. monocytogenes. In contrast, antibacterial activities were highest against S. paratyphi, P. mirabilis and E. coli with a mean concentration of 20.8, 18.8 and 15.7µl/ml, respectively. P. aeruginosa was found to be the most sensitive bacteria to all essential oils showing MIC of 0.1 to 1.6 with overall mean values of 0.62µl/ml while K. pneumonia ranked next with MIC mean values of 1.36µl/ml. The mean MIC values of the essential oils against B. cereus were significantly higher than the control (P= 0.013) whereas the essential oils against L. monocytogenes and S. aureus had comparable antibacterial activity with the control drug (P>0.05). The mean of MIC values were significantly higher against Gram-positive than Gram-negative bacteria (P<0.001).