Thymus schimperi Ronninger (Lamiaceae) locally known as Tosign, is a multipurpose endemic plant that has been used for various remedies as constituents of traditional medicine in Ethiopia. The objective of this study is to evaluate antibacterial activity of water, ethanol, methanol and chloroform extracts of T. schimperi using agar well diffusion and broth dilution methods against human pathogenic bacterial strains. Amongst the solvents used for this study, chloroform extract possess the highest potential of inhibiting the growth of all bacteria under study at concentrations of 50 mg/ml while ethanol and methanol extract fail to inhibit three gram negative bacteria, namely: Escherichia coli (ATCC 25922), Klebsiella pneumoniae (clinical isolate) and Shigella flexneri (ATCC 12022) at the same concentration. Water extract did not show any zone of inhibition on all test bacteria as compared to other solvents. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were performed only for chloroform extracts that showed inhibition against all test organisms. This study revealed that, the highest inhibition with chloroform extract was exhibited against Methicillin-Resistant S. aureus (MRSA) with mean zones of inhibition of 22.6+2.5 mm whilst the minimum inhibition zone was observed for E. coli with mean zone of inhibition of 14.6+2.3 mm. The MIC value ranged from 6.25 to 12.5 mg/ml while the MBC value ranged from 6.25 mm to 25 mg/ml. This study clearly indicates that the crude chloroform extract of T. schimperi showed highest antibacterial activity against all studied bacterial strains as compared to the three solvents used in this study. Thus, further study and characterization of active compounds of chloroform extract of this plant is required.
Key words: Antibacterial activity, MBC, MIC, Thymus schimperi, Tosign, zone of inhibition.
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