Antibacterial activities and ciprofloxacin potentiation of Melissa officinalis extracts against some gram negative pathogenic bacteria

In bacteria using inhibitors of efflux pumps (EPIs) is one of several strategies to combat with bacterial resistance. It is well documented that most medicinal plants especially those with antimicrobial properties composed of elements (EPIs) that disturb the efflux pumps of bacteria. The current work was designed to evaluate antibacterial activities of ethanol and chlorophorm extracts of Melissa officinalis and also synergistic effects of the extracts with ciprofloxacin against some gram negative pathogenic bacteria. We also examined the inhibitory effects of the extracts on efflux pumps. Minimum inhibitory concentrations (MICs) of the extracts alone or in association with ciprofloxacin or phenylalanine arginine β- naphtylamide (PAβN) were determined using broth micro dilution method. Effects of the extracts on efflux pumps of the examined bacteria detected by using ethidium bromide in well diffusion assays. The extracts from M. officinalis showed antibacterial activities against all examined bacteria in a range of 3125 to 25000 μg/mL as determined by MIC determination. The extracts from M. officinalis showed synergistic effects with ciprofloxacin on Salmonella enteritidis and Escherichia coli. In Pseudomonas aeruginosa and Acinetobacter baumannii PAβN had no effect on MIC of ciprofloxacin but the association of extracts decreased it. In S. enertidis and E Coli both extracts of M. officinalis increased the amount of ethidium bromide accumulation (i.e. reduced efflux). The overall results show that associations of fluoroquinolones with extracts of M. officinalis may potentiate the antibacterial effects of fluoroquinolones.