Identification and Characterization of Two Antibacterial Compounds Extracted from Thuja arborvitae

Thuja arborvitae are widely grown in North America and East Asia for their ornamental value, and their leaf oil extracts have been used to treat bacterial infections. This study aimed to identify antibacterial compounds from Thuja leaves. The methanol extract of Thuja leaves exhibited strong antibacterial activity against Gram-positive (Staphylococcus aureus and Streptococcus mutans) and Gram-negative (Acinetobacter baumannii, Pseudomonas aeruginosa) bacteria. The major compounds in the active fractions were isolated and identified as apigenin-7-di-p-coumarylglucoside and eicosapentaenoic acid. The identified compounds showed potent antibacterial activity against the four tested microorganisms with IC50 values of 10 to 50 µg/mL. More importantly, these compounds showed potent inhibitory activity (IC50: 10 μg/mL) against the multidrug-resistant bacterial strain Acinetobacter baumannii. Two antibacterial compounds are now being reported for the first time in Thuja arborvitae, and they may have potential for the treatment of bacterial infections.