Abstract
BackgroundThe continuous emergence of multi-drug-resistant bacteria drastically reduces the efficacy of antibiotic armory and, consequently, increases the frequency of therapeutic failure. The discovery of new antibacterial drugs is an urgent need. The present study reports the antibacterial and antioxidant activities of the methanol extract, fractions and iridoids from Canthium subcordatum, a plant traditionally used as antidiabetic, anti-inflammatory, and antimicrobial.MethodsBroth microdilution assay was used to determine minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs) of extracts and iridoids against Staphylococcus aureus, Vibrio cholerae and Shigella flexneri. Antioxidant activity was evaluated using 1,1-diphenyl-2-picrylhydrazyl (DPPH) and gallic acid equivalent antioxidant capacity (GAEAC) assays. The samples were also tested for their cytotoxicity against human red blood cells (RBC).ResultsThe methanol extract, hexane, ethyl acetate and iso-butanol fractions from C. subcordatum fruits displayed different degrees of antioxidant (EC50 = 62.83–70.17 μg/ml; GAEAC = 45.63–58.23 μg/ml) and antibacterial (MIC = 128–512 μg/ml) activities. Canthiumoside 1(1) and linearin (7) were the most active antioxidant (EC50 = 1.12–2.03 μg/ml; GAEAC = 79.82–92.35 μg/ml) and antibacterial (MIC = 8–64 μg/ml) compounds while the most sensitive bacterium was Staphylococcus aureus. The tested samples were non-toxic to normal cells.ConclusionOur results demonstrated that compounds 1 and 7 were potent antibacterial agents and DPPH/ABTS·+ radical scavengers, so they warrant further investigation.
Highlights
The continuous emergence of multi-drug-resistant bacteria drastically reduces the efficacy of antibiotic armory and, increases the frequency of therapeutic failure
Antibacterial activity In the present work, the extracts as well as 12 compounds isolated from the fruits of C. subcordatum were tested for their antibacterial activities against Vibrio cholerae, Shigella flexneri and Staphylococcus aureus (Table 1)
The minimum inhibitory concentration (MIC) results indicated that the MeOH extract, n-BuOH and Ethyl acetate (EtOAc) fractions as well as compounds 1, 2, 5a and 6–9 inhibited the growth of all tested bacterial species
Summary
The continuous emergence of multi-drug-resistant bacteria drastically reduces the efficacy of antibiotic armory and, increases the frequency of therapeutic failure. The present study reports the antibacterial and antioxidant activities of the methanol extract, fractions and iridoids from Canthium subcordatum, a plant traditionally used as antidiabetic, anti-inflammatory, and antimicrobial. Previous phytochemical works on this plant species and other Canthium species revealed the presence of iridoids [8,9,10], iridoid peptidic alkaloids [11, 12], flavonoids [10], terpenoids and miscellaneous [12, 13] It is not yet known which of the phytoconstituents is responsible of the antimicrobial effect of this plant, when it is used to cure infectious diseases and oxidative stress conditions. The present study reports the antibacterial and antioxidant activities of extracts and iridoids from C. subcordatum fruits
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