Antimicrobial and antioxidant activity of the crude leaf extracts of Pycnostachys urticifolia Hook. (Lamiaceae)

Pycnostachys urticifolia is an ethnomedicinal plant indigenous to South Africa. Its crude leaf extracts possess phenolics, alkaloids, flavonoids, terpenoids and saponins amongst other bioactive compounds. This study compared the antimicrobial and antioxidant activities of young and mature leaf extracts obtained by soxhlation and cold sonication. Evaluation of the antimicrobial activity of hexane, chloroform and methanol extracts were performed against Gram-positive and Gram-negative bacteria and fungi by the microdilution method [1]. The antioxidant activity of 50% methanol extracts was assessed using the ferric-reducing antioxidant power (FRAP), DPPH radical scavenging and β-carotene-linoleic acid model assays [2]. Good antimicrobial activity against all bacteria and fungi was exhibited by the soxhlated chloroform extracts of young and mature leaves (between 0.156 and 0.625 mg/mL). The FRAP activity of soxhlated extracts was greater than cold sonicated extracts in a dose-dependent manner (between 0.078 and 1.25 mg/mL). Mature leaves showed greater FRAP activity than young leaves irrespective of the extraction method (< 0.3125 mg/mL). A greater DPPH radical scavenging activity was observed in mature leaf extracts compared to that of the young. All extracts presented noteworthy antioxidant activity compared to butylated hydroxytoluene based on the rate of β-carotene bleaching (73.1 – 95.9%). Pycnostachys urticifolia possesses considerable antimicrobial and antioxidant activity that validates the traditional use of this species.

References:

[1] Ndhlala AR, Mulaudzi R, Ncube B, Abdelgadir HA, du Plooy CP, Van Staden J. Antioxidant, antimicrobial and phytochemical variations in thirteen Moringa oleifera Lam. cultivars. Molecules 2014; 19: 10480 – 10494

[2] Moyo M, Ndhala AR, Finnie JF, Van Staden J. Phenolic composition, antioxidant and acetylcholinesterase inhibitory activities of Sclerocarya birrea and Harpephyllum caffrum (Anacardiaceae) extracts. Food Chem 2010; 123: 69 – 76