The surface extract of an accession of Psiadia punctulata (DC.) Vatke (Asteraceae) growing in Saudi Arabia was investigated for its phytochemical composition. A bio-guided investigation of the extract led to the isolation of thirteen ent-kaurane and trachylobane diterpenes and seventeen compounds previously described, including nine flavonoids and eight diterpenes. Three flavonoids and one ent-kaurane diterpene showed antimicrobial activity with MIC100 values ranging from 25 to 150 μg/ml. The extract showed antibacterial activity against Staphylococcus aureus (MIC100 = 180 μg/ml) and antifungal activity against Candida albicans (MIC0 = 130 μg/ml). The isolated 3',4',5,7-tetramethoxyflavone, at a concentration of 40 μg/ml, displayed the ability to reduce biofilm formation of S. aureus and C. albicans by 50% and 90% respectively.
Keywords: Antimicrobial activity; Asteraceae; Kaurane; Psiadia punctulata; Trachylobane.
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