RESUMO
The emergence of fungal resistance to commercial drugs has been a major problem for the WHO. In this context, research with natural products is promising in the discovery of new active substances. Thus, this work evaluated the antifungal effect of a medicinal plant (i.e., Mesosphaerum suaveolens) against strains of the genus Candida, tested the combined effect with the drug fluconazole, and, finally, determined the phenolic constituents present in the species. Initially, aqueous extracts of leaves (AELMs) and aerial parts (AEAPMs) of the species were prepared. For microbiological assays, the minimum fungicidal concentration was determined by broth microdilution, and the combined effect of fluconazole extracts were verified by sub-inhibitory microdilution concentrations (CFM/8) followed by spectrophotometric readings which were used to determine the IC50. HPLC detected the presence of flavonoids and phenolic acids, detecting eight compounds present in the samples of which caffeic acid and quercetin were major components. The AELMs modulated fluconazole activity since it decreased fluconazole's IC50 from 7.8 µg/mL to an IC50 of 4.7 µg/mL (CA LM 77) and from 28.8 µg/mL to 18.26 µg/mL (CA INCQS 40006) for the C. albicans strains. The AEAPMs were able to potentiate the effect of fluconazole more effectively than the AELMs. Such an effect was significant for the 16 µg/mL concentration for CA LM 77 and 32 µg/mL for CA INCQS 40006. The AEAPMs as well as the AELMs presented clinically relevant activities for C. tropicalis strains. For the C. tropicalis LM 23 strain, the AEPMs obtained an IC50 of 25 µg/mL and the AELMs an IC50 of 359.9 µg/mL.
RESUMO
The present study aimed to evaluate the antibacterial and modulatory potential of α-bisabolol, ß-cyclodextrin and α-bisabolol/ß-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 ß-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 ß-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 ß-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.
