Aim: This work aimed to evaluate the biological activity of the leaf extracts of Juniperus thurifera L., which is an Algerian endemic tree that belongs to the family of Cupressaceae.

Materials and Methods: The plant leaves were extracted in solvents of increasing polarity to obtain different extracts such as methanol, petroleum ether, chloroform, ethyl acetate, and aqueous extracts (MeE, PEE, ChlE, EtAE, and AqE). The antioxidant activity of four extracts (MeE, ChlE, EtAE, and AqE) was assessed by trapping test of 1,1-diphenyl-2- picrylhydrazyl (DPPH) radical. The evaluation of antibacterial activity of MeE, ChlE, EtAE, and PEE was done using the disk diffusion method on solid agar.

Results: The three extracts of EtAE, AqE, and MeE showed high antiradical activity toward the DPPH radical (IC₅₀=29.348 μg/mL, 37.538 μg/mL, and 52.573 μg/mL, respectively), while the lowest radical scavenging activity was expressed by the ChlE (IC₅₀=70.096 μg/mL). These extracts were active only toward the Gram-positive bacteria (Staphylococcus aureus ATCC and methicillin-resistant S. aureus) at different concentrations, and the highest activity was obtained with the ChlE with an inhibition diameter of 14 mm at the concentration of 1 g/mL. No inhibition was detected for all of these extracts against the Gram-negative tested strains (Escherichia coli ATCC, Pseudomonas aeruginosa ATCC, and Enterobacter cloacae (extended spectrum β-lactamase).

Conclusion: From this study, on the one hand, it was concluded that J. thurifera L. leaves extracts exhibited a very intense antioxidant potential toward the DPPH radical, and on the other hand, the antibacterial activity showed an action spectrum exclusively toward the Gram-positive bacteria.

Keywords: antibacterial activity, antioxidant activity, extraction, Juniperus thurifera L., trapping test of 1,1-diphenyl-2- picrylhydrazyl radical.

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