The antimicrobial effects of specific herbs against common bacteria.
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With bacteria building increased resistance to antibiotics, research of traditional medicine has increased dramatically, especially in regards to the use of herbal substances as antimicrobial agents. It has been discovered that some herbal substances have similar beneficial effects on the human body as some non-herbal medicines, yet possess a smaller concentration of harmful chemical substances, and exhibit fewer side effects.
In this study six different herb extracts (fenugreek, fennel, ajowan, wild rue, yarrow, and pennyroyal) were tested for antimicrobial activity against five different common bacteria (Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Enterococcus faecalis, and Acinetobacter). To determine which solvent extracted the highest antimicrobial agents the herbs were ground and extracted in three different solvents: acetone, methanol and ethanol. Extraction was done for three days at room temperature after which each extract was filtered through a 0.22 uM filter to remove any debris.
Broth and agar dilution methods were used to determine the minimal inhibitory concentration (MIC) of the six herbal extracts. For the broth dilution method, doubling dilutions of the extracts were done in a 96 well plate containing Luria-Bertani (LB) broth. Bacteria grown in LB broth was added to the plates. The plates were incubated overnight at 37oC. Due to the cloudy nature of the extracts it was not possible to determine the MIC from the 96 well plate. Thus each well from the 96 well plates was stamped onto an agar plate and the agar plates were incubated overnight at 37oC. From the agar plates the antimicrobial activity of the extracts was deducible and the MIC determined. After assessing the lowest concentration of the antimicrobial agents that inhibited visible growth of the tested we were able to narrow down our antimicrobial agents for each bacterium.
To further test if any of the extracts were synergistic with common antibiotics we then determined the MIC of the bacterial strains for 12 different antibiotics. Once the MIC was determined, checker board method in 96 well plate format was used to test synergy between the extracts and antibiotics. Doubling dilutions of the antibiotics were added to the plate in a horizontal format and doubling dilutions of the extracts were added in a vertical format. Bacteria was the added to each well. The plates were incubated at 37oC overnight and stamped on agar plates the next day. Agar plates were incubated at 37oC overnight. Thus, we were able to evaluate the antimicrobial potentials of the examined herbs.