Comparative study of the inhibitory efficacy of some medicinal plant oils on the growth of pure isolates from a group of pathogenic microorganisms in vitro

The present in vitro study was undertaken to evaluate the antimicrobial efficacy of essential oils of four medicinal plants including: Eugenia caryophyllus, Sesamum indicum, Linum usitatissimum, and Mentha piperita against the growth of seven pathogenic microorganisms: two gram-positive bacteria; Staphylococcus cohnii cohnii, Micrococcus spp., and five gram-negative bacteria; Pseudomonas aeroginosa, Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, and Enterobacter cloacae. The method employed to test the antimicrobial efficacy was the Agar Well Diffusion test. The antimicrobial activity of Eugenia caryophyllus oil against the growth of all the test microorganisms except Proteus mirabilis was statically superior to the rest of the test oils with mean diameter of zone of inhibition; 28.5±0.87 mm, 12.25±0.25 mm, 22.25±0.66 mm, 23.08±1.16 mm, 27.83±1.39 mm, and 10.91±0.39 mm against the growth of Staphylococcus cohnii cohnii, Micrococcus spp., Pseudomonas aeroginosa, Escherichia coli, Klebsiella pneumoniae, and Enterobacter cloacae respectively. Sesamum indicum oil produce significant effect against Pseudomonas aeroginosa and Proteus mirabilis with mean diameter of zone of inhibition; 21.75±1.29 mm and 14.25±1.03 mm respectively. Linum usitatissimum revealed positive results against Micrococcus spp. Only with mean diameter of zone of inhibition; 30.41±0.46 mm. while the oil of Mentha piperita did not show any inhibitory activity against each of the test microorganisms