Screening of Indian medicinal plants as efflux pump inhibitors of fluoroquinolones

Efflux mechanisms have become broadly recognized as major components of resistance to many classes of antibiotics. Efflux related multidrug resistance (MDR) is a significant means by which bacteria can evade the effects of antibacterial agents. This study sought to give a scientific basis to plants already used for traditional purposes as bacterial efflux pump inhibitors (EPIs). A decline in minimum inhibitory concentration (MIC) 1/2 to 1/8 was used to determine the activity of 35 Indian medicinal plant extracts as drug EPIs against various bacterial strains. Fluoroquinolones (ciprofloxacin and ofloxacin) possesses antibacterial activity and when combined with plant extracts resulted in synergistic interactions by declining its MIC to 1/2 in 10 plants and 1/4 in 6 plants. Methanolic extracts of twelve plants were found to be putative EPI hence, the compounds in these extracts can serve as templates of new antibacterial agents. Plant extracts significantly enhanced accumulation and decreased the efflux of fluoroquinolones in bacterial strains, suggesting their ability to inhibit bacterial efflux pumps. EPI reduced the ciprofloxacin and ofloxacin MIC by 1/4 in 3 and 1 strains respectively. Our data support the fact that increased fluoroquinolones usage can negatively impact susceptibility of bacterial strains. Plants should be further exploited for their potential to produce compounds capable of blocking the mechanism of efflux.