Combined antibacterial effect of essential oils from three most commonly used Ethiopian traditional medicinal plants on multidrug resistant bacteria

BACKGROUND: An alarm increase the rate of emerging and re-emerging of multidrug resistant bacteria have been caused great public health concern in the worldwide. They have been resisting for most or majority of currently available and affordable antibiotics and imposed socioeconomic catastrophe at global scale. As a result, there is utmost important to discover new or modify currently available antibiotics. The aim of this study was to evaluate combined antibacterial effect of essential oils obtained from Blepharis cuspidata, Boswellia ogadensis and Thymus schimper against multidrug resistance (MDR) Escherichia coli, Klebsiella pneumoniae and Methicillin resistant S. aureus. METHODS: Essential oil (EO) was extracted from the aerial part of B. cuspidata, B.ogadensis and T. schimper by steam distillation and stored in brown bottles at 4 °C. There were mixed in 1:1 ratio and adsorbed to disc and placed on MHA and measured their minimum inhibitory zone seeded with E. coli, K. pneumoniae and MRAS after 18-24 H. minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were measured by broth micro-dilution method. The interaction between EOs was determined by fractional inhibitory concentration index. RESULTS: The antibacterial potential of mixed oil depends on the doses and type of the EOs and bacteria species. The combined EOs of B.cuspidata and T.schimperi had inhibition zone (39 mm), its MIC and MBC value was 0.39 μl/ml against MRSA. It had inhibition zone (28-35 mm), MIC value 0.39–6.25 μl/ml and MBC (0.78–12.5 μl/ml) against MDR E. coli and K. pneumoniae. Whereas, combined effects of B. cuspidata and B. ogadensis had MIC values ranges from 0.78–6.25 μl/ml for E.coli and K. pneumoniae and 1.56 μl/ml for MRSA. There was strong synergistic effect between the combination of B.cuspidata and T.schimperi. This study revealed that gram negative bacteria were slightly less susceptible than gram positive. CONCLUSIONS: This in vitro study of combined EOs has significant antibacterial effect than using each of them and even it was more potent antibacterial effect on MDR as compare to modern antibiotics. Hence, it can be applied to a pharmaceutical composition as modulator or adjuvant or precursor for synthesis of new antibiotic in future activities.