Objective: Traditional antibiotics are increasingly suffering from the emergence of efflux related multidrug resistance (MDR) amongst pathogenic bacteria that led to novel approaches to control microbial infections being investigated as potential alternative treatments. Synergism between natural sources and antibiotics has received much attention and efforts have been put in to identify compounds that can act as efflux pump inhibitors.
Methods:Methanol and ethyl acetate extracts of important medicinal plant species widely used in traditional remedies for various ailments were screened for their synergism with ciprofloxacin and tetracycline antibiotics using the agar well diffusion method. Phytochemical analysis was also done by standard methods. In addition, to evaluate the potential of synergistic extracts as efflux pump inhibitors against Salmonella enterica serovar Typhimurium (S. Typhimurium) strains, including wild-type (NKS70), overexpressed AcrAB (NKS773) as well as against knockout TolC (NKS174), berberine uptake and ethidium bromide inhibition assays were done.
Results:In vitro synergistic activity were confirmed for methanolic extracts of all five plants, namely, Allium sativum (Amaryllidaceae), Syzygium aromaticum (Myrtaceae), Berberis aristata (Berberidaceae), Rhus cotinus (Anacardiaceae), and Phyllanthus emblica (Phyllanthaceae). Agar well diffusion method confirmed the greatest synergistic activity of P. emblica with used antibiotics. The phytochemical analysis of medicinal plants showed that the terpenoids and reducing sugar were found to be present in all synergistic extracts. Phytochemicals have great potential as antimicrobial agents. Further efflux inhibition assays confirmed maximum efflux pump inhibition through Phyllanthus emblica extract against S. Typhimurium when extracted with methanol solvent.
Conclusion:It is hypothesized that phyto compounds present in these plants might be following the same mechanism of action responsible for synergistic interaction as well as efflux inhibition. These data provide bioactive compounds for possible clinical utility as efflux inhibitors.