Abstract

Objective: To investigate phytochemical constituents, antibacterial and antioxidant activity of the root extracts of Carduus macracanthus (C. macracanthus). Methods: Phytochemical screening tests were conducted as per of the standard procedure to identify the classes of compounds present in the root extract of C. macracanthus. Silica gel column chromatographic technique was applied to separate the constituents from chloroform/ methanol (1:1) root extracts. Various spectroscopic techniques were applied to determine the structure of the isolated compound. In vtiro antibacterial activities of crude extracts were evaluated via disc diffusion method. Minimum inhibitory concentration and minimum bacterial concentration were determined by broth dilution method. Moreover, antioxidant activities of extracts were determined by DPPH assay, the phosphomolybdenum method and total flavonoid contents were determined as per of the standard procedures. Results: Phytochemical screening of root extracts of C. macracanthus revealed the presence alkaloids, flavonoids, triterpenes, tannins and steroids. Silica gel column chromatography separation of root extract using chloroform/methanol (1:1 ratio) yielded a known plant steroid stigmasterol. The result revealed that methanol extract had the greatest DPPH scavenging (IC50 = 97.50 ± 4.38 μg/mL) and total antioxidant (1.92 ± 0.24 mg AAE/g of dried extract) activities. Chloroform/methanol (1:1), and methanol extracts showed that growth suppression of Bacillus cereus and Staphylococcus aureus at a concentration above 25 mg/mL, and minimum inhibitory concentration was found to be 25 mg/mL. Methanol extract showed growth suppression against Escherichia coli at a concentration of 50 mg/mL. The antibacterial activities of the extracts were compared with a commercially available antibiotic (chloramphenicol) and showed moderate antibacterial activities, with inhibition zones ranging between 18–28 mm. However, the extracts had no antibacterial effects on Salmonella typhi. Conclusions: The present study found that polar extracts of the root of C. macracanthus possessed antibacterial and antioxidant activities.

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