Evaluation of the antibacterial and modulatory potential of α-bisabolol, β-cyclodextrin and α-bisabolol/β-cyclodextrin complex.

The present study aimed to evaluate the antibacterial and modulatory potential of α-bisabolol, β-cyclodextrin and α-bisabolol/β-cyclodextrin complex. The minimum inhibitory concentration was determined through the broth microdilution technique using the bacterial strains: Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa. The drugs norfloxacin, imipenem and gentamicin were used in the tests, and the compounds α-bisabolol and β-cyclodextrin; all the compounds were diluted in DMSO. To obtain the minimum inhibitory concentration (MIC) a serial microdilution of the substances in volumes corresponding to the sub-inhibitory concentration (MIC/8), and microdilution with the antibiotic until the penultimate well were performed. The results showed that β-cyclodextrin did not present synergistic effects when combined with the antibiotics. It was found that α-bisabolol presented a synergistic effect against S. aureus, when combined with the antibiotic norfloxacin. Moreover, α-bisabolol presented synergism against E. coli when combined with gentamicin. The results of this study show that α-bisabolol presents a modulatory synergistic effect for some antibiotics, as gentamicin, and this is an interesting result against multidrug resistant bacteria (MDR). By other side, the complexation of α-bisabolol with β-cyclodextrin apparently reduces the modulatory effect, maybe due the polarity enhancement of the polarity of α-bisabolol, affecting the interaction of this compound with the cell membrane bilayer. However, more studies are necessary to demonstrate or not these interactions.