Antibacterial activity and antibiotic-modifying action of carvacrol against multidrug-resistant bacteria

Bacterial resistance is a serious health problem, which is mostly caused by the inappropriate use of antibiotics. The emergence of strains resistant to these drugs results in difficulties in the treatment of bacterial infections. Therefore, it has been a trend to investigate new alternatives against microbial resistance such as the use of natural products and their major compounds. The monoterpene carvacrol which is mostly extracted from essential oils has been pointed as a promisor. In the search for better results in terms of pharmaceutical applications of associations and complexes, β-cyclodextrin has been promising when complexed with isolated compounds. This study aimed to evaluate the antibacterial activity of the compound carvacrol, pure and complexed with β-cyclodextrin, against the strains of Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli. The antibacterial activity assay was performed using the broth microdilution method, determining the minimum inhibitory concentration (MIC), and from the subinhibitory concentration value (MIC/8) was evaluated the modifier activity of the antibiotic action. The reading of the tests was carried out using sodium resazurin and expressed by geometric mean. Carvacrol showed significant results against standard bacteria: S. aureus with a MIC of 81 μg/mL, and P. aeruginosa with a MIC of 161 μg/mL. Also, a MIC of 128 μg/mL for the multidrug-resistant strain of P. aeruginosa. Regarding the modifier effect on antibiotic action when associated with gentamicin, complexed carvacrol showed synergism against E. coli, with a reduction in the MIC from 25 μg/mL to 5 μg/mL. Carvacrol demonstrated relevant clinical antibacterial activity, for both gram-positive and gram-negative bacteria, and a synergistic effect when associated with gentamicin. Therefore, these results showed to be promising in fighting bacterial resistance.