Abstract
The increase in antibiotic resistance and the emergence of new bacterial infections have intensified the research for natural products from plants with associated therapy. This study aimed to verify the antibacterial and antioxidant activity of crude extracts of the genus Plectranthus species, being the first report on the modulation of aminoglycosides antibiotic activity by Plectranthus amboinicus extracts. The chemical composition was obtained by chemical prospecting and High-Performance Liquid Chromatography with diode arrangement detector (HPLC/DAD). The antibacterial activities of the extracts alone or in association with aminoglycosides were analyzed using the microdilution test. The antioxidant activity was evaluated by 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging. The phytochemical prospection allowed the flavonoids, saponins, tannins and triterpenoids to be identified. Quercetin, rutin, gallic acid, chlorogenic acid, caffeic acid, catechin, kaempferol, glycosylated kaempferol, quercitrin, and isoquercitrin were identified and quantified. The principal component analysis (PCA) observed the influence of flavonoids and phenolic acids from Plectranthus species on studied activities. Phytochemical tests with the extracts indicated, especially, the presence of flavonoids, confirmed by quantitative analysis by HPLC. The results revealed antibacterial activities, and synergistic effects combined with aminoglycosides, as well as antioxidant potential, especially for P. ornatus species, with IC50 of 32.21 µg/mL. Multivariate analyzes show that the inclusion of data from the antioxidant and antibacterial activity suggests that the antioxidant effect of these species presents a significant contribution to the synergistic effect of phytoconstituents, especially based on the flavonoid contents. The results of this study suggest the antibacterial activity of Plectranthus extracts, as well as their potential in modifying the resistance of the analyzed aminoglycosides.
Highlights
IntroductionAmong the plant species most widely used in the treatment of diseases and ethnobotanical applications, the genus Plectranthus (Lamiaceae) should be highlighted; it is widely studied in ethnopharmacological and chemical terms, as it has a representative popular use in the form of teas, infusions, and syrups, especially in the treatment of digestive, dermatological, and respiratory diseases [4,5]
The results prove that the extracts contained among other compounds, as shown in Figure 1, gallic acid (Rt = 13.87 min, peak 1), catechin (Rt = 19.94 min, peak 2), chlorogenic acid (Rt = 24.15 min, peak 3), caffeic acid (Rt = 27, 45 min, peak 4), rutin (Rt = 39.83 min, peak 5), quercitrin (Rt = 42.28 min, peak 6), isoquercitrin (Rt = 45.06 min, peak 7), quercetin (Rt = 48.35 min, peak 8), kaempferol (Rt = 57.62 min, peak 9) and glycosated kaempferol (Rt = 66.31 min, peak 10)
The results show that all extracts showed DPPH free radical scavenging activity
Summary
Among the plant species most widely used in the treatment of diseases and ethnobotanical applications, the genus Plectranthus (Lamiaceae) should be highlighted; it is widely studied in ethnopharmacological and chemical terms, as it has a representative popular use in the form of teas, infusions, and syrups, especially in the treatment of digestive, dermatological, and respiratory diseases [4,5]. The Plectranthus genus includes about 300 species of herbs and shrubs native to tropical and warm regions worldwide [6]. Its bioactivities are related to its content of phenolic compounds, proving to be rich in flavonoids, especially flavones, flavonols and flavonones, and phenolic acids, such as trans-rosmarinic acid [4,9,10,11,12]
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