Abstract:
The threat of pathogenic infections has almost been eradicated with the introduction of antibiotic treatment regimes. Unfortunately, the repetitive consumption and increasing doses of antibiotics have led to the manifestation of drug tolerance and resistance in microorganisms due to the natural selection process. As a result of this phenomenon, new antibiotics would need to be developed in order to overcome this tolerance/resistance. In this study, antibacterial effects as a result of the preliminary screening between several commercially available essential oils and beta-lactam antibiotics were investigated on multidrug resistant bacteria followed by the modes of action for resistance reversal capability in some of these essential oils.
Out of 35 antibiotic-essential oil pairs tested, four showed synergistic effect (FIC ≤ 0.5) and 31 showed no interaction (FIC > 0.5 – 4.0). The preliminary results obtained highlighted the occurrence of a pronounced synergistic relationship between piperacillin/cinnamon bark oil, piperacillin/lavender oil, piperacillin/peppermint oil as well as meropenem/peppermint oil against Escherichia coli J53 R1 and E. coli J53 pMG309 respectively with FIC index in the range 0.26 – 0.5. The time-kill method was used to evaluate the bactericidal activities of essential oils alone or with antibiotics. A rapid and complete killing of bacteria was observed in piperacillin/peppermint, piperacillin/lavender and meropenem/peppermint combinations within 5 – 10 minutes of exposure time. Piperacillin/cinnamon bark combination showed a complete killing profile after 20 h of exposure. Analysis of the membrane permeability effects of essential oils on treated cultures through their stability against sodium dodecyl sulfate demonstrated that essential oils played a role in disrupting the bacterial cell membrane. The action of essential oils on membrane integrity was also confirmed through the decrease in the negative charge of cell surfaces. In addition, the morphology of cells post-treatment with essential oils alone and in combination with antibiotics showed corrugated surfaces and irregular rod-shaped forms under scanning electron microscopic analysis.
The overall study emphasised the potential of peppermint, cinnamon bark and lavender essential oils as potential sources of new multi-targeted antimicrobial products. Reduction in the dosage of antibiotics could be employed as a treatment strategy to combat the onset of antibiotic resistance as well as to decrease its adverse effects.
