Investigation of Antimicrobial Activity of Medicinal Plant Extracts on Bacillus cereus Isolated from Soil

Abstract

Background: Because many plant extracts have a significant inhibitory effect on pathogenic microorganisms, so we aimed to evaluate the antioxidant and antimicrobial activity of some plant extracts on Bacillus cereus isolated from soil. Methods: The chicory (Cichorium intybus L.), hyacinth (Hypericum perforatum L.), lavender (Lavandula angustifolia), yew (Taxus baccata), and thyme (Thymus vulgaris L.) plants were collected and identified in the botanical laboratory of the University of Zabol. To prepare the ethanolic extract, 40 g of dried leaves of plants were used in 400 cc of ethanol. Different strains of B. cereus used in this study were isolated from soil and identified by biochemical, bacteriological, and growth tests as well as standard tests. Antimicrobial effects were investigated by diffusion method in Müller Hinton agar medium using 6 mm paper discs according to Bauer and Kirby instructions as well as microdilution. Statistix ver10 software was used for statistical calculations. Mean comparisons were performed using the LSD at the 1% level, and Excel was also used to draw the figures. Results: The diameter of the growth inhibition zone of plant extracts against B. cereus at a dilution of 100 ppm was investigated, and it was found that different extracts had different effects on inhibiting the growth of B. cereus (P < 0.01). LSD test showed that thyme (T. vulgaris L.) had the highest (15 mm) effect on growth inhibition of strains 2 and 3 of B. cereus and the lowest (1 mm) effect on growth inhibition of strain 1 of B. cereus. The lowest minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of thyme (T. vulgaris L.) against B. cereus samples were 3.1 and 6.2 ppm, respectively. Conclusions: Considering the side effects of chemical drugs and antibiotics, as well as the potential effect of medicinal plant extracts, especially T. vulgaris L. on B. cereus, it is recommended that T. vulgaris L. may inhibit the growth of B. cereus.