Antimicrobial and antibiofilm potential of Eucalyptus globulus and Mentha piperita L. and the association with commercial antimicrobials

Abstract

The inappropriate use of antimicrobials in human and veterinary medicine results in the selection of multidrug-resistant strains, which have become a health problem and imposes the search for safe and effective factors that can be used in the treatment of persistent bacterial infections. In this context, studies with plants and their use in combinatorial therapies have been recently stimulated. This study aims to evaluate the antibacterial and antibiofilm potential of essential oils (EO) from Eucalyptus globulus and Mentha piperita L. against Gram-positive and Gram-negative bacteria, and their interactions with commercial antimicrobials. The antimicrobial potential was evaluated by the disk diffusion method and the minimum inhibitory concentration (MIC) determined by broth microdilution. The biofilm formation ability was evaluated in a 96-well microplate, using crystal violet methodology. Association assays between EO and antimicrobials were performed using the disk-diffusion method. The bacterial strains showed sensitivity to the EO tested, except for P. aeruginosa. The EO were still able to inhibit the adhesion of bacterial cells in the first stage of formation in all bacteria tested. Regarding the association with antimicrobials, the interactions varied according to the EO and the bacterial strain tested. A total of 14 interactions were observed, being 11 synergistic and 3 antagonistic. The highest number of synergistic interactions (8) was observed against Gram-negative strains, whereas antagonistic interactions were observed only against Gram-positive (3). Four synergistic interactions were observed against P. aeruginosa, a relevant finding since this species shows intrinsic drug resistance.