Antimicrobial activity of <i>Aloysia polystachya</i> essential oil. Characterization and antibacterial mechanism analysis on planktonic bacteria and biofilms

The antimicrobial activity of essential oils (EOs) has attracted increasing attention. Therefore, this study aimed to assess the antimicrobial activity of an EO extracted from <i>Aloysia polystachya</i> located in Santiago del Estero, in the northwestern region of Argentina, against <i>Escherichia coli</i> and <i>Staphylococcus aureus</i>. First, the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of the EO were determined. Although both bacteria had the same MIC (40 µL/mL), only the MBC of <i>E. coli</i> was found (80 µL/mL). According to the death curves, after only 1 h of incubation, the 2× MIC of EO eliminated 100% of the bacteria on <i>E. coli</i>, and 90% of the bacteria on <i>S. aureus</i>. To elucidate the mechanism of action, membrane permeabilization was evaluated. Our results showed that in both bacteria tested, the EO was able to induce permeabilization of the bacterial membrane. Finally, the EO inhibited biofilm formation and eradicated preformed biofilms of both bacteria tested. It can be concluded that EO has antibacterial activity against planktonic bacteria and the biofilms of both bacteria studied. These results describe the promising antimicrobial efficacy of <i>A. polystachya</i> EO and the potential mechanism by which membrane permeabilization plays a critical role.