Modulation of Fluoroquinolone Resistance by Lippia Origanoides Kunth in Staphylococcus Aureus

In this study, the ethanolic extract, and the dichloromethane fraction from L. origanoides were assessed for their antibacterial activity alone or in combination with fluoroquinolones against a S. aureus strain resistant to hydrophilic fluoroquinolones due to overexpression of the norA gene encoding the NorA efflux pump, aiming to investigate the occurrence of efflux pump inhibitors in this plant. Minimal inhibitory concentrations (MICs) and modulatory activity on resistance to fluoroquinolones of the extracts were determined by a micro-dilution assay. The ethanolic extract showed weak anti-staphylococci activity, while the dichloromethane extract demonstrated moderate antimicrobial activity against the strains tested. The addition of ethanolic and dichloromethane extracts to the growth medium at sub-inhibitory concentrations enhanced the activity of norfloxacin and ciprofloxacin, as well as ethidium bromide, against S. aureus SA1199-B overproducing NorA. L. origanoides can be a source of secondary metabolites able to inhibit the S. aureus NorA efflux pump.