Chemical Composition and Antibacterial Activity of Essential Oils from Different Organs of Pistacia falcata.

Pistacia falcata Becc. ex Martelli (Anacardiaceae) is a medicinal species distributed across parts of the Middle East and Africa. This study characterized the essential oils from different organs of P. falcata and evaluated their antibacterial and antibiofilm activities. Essential oils from leaves, roots, inflorescences and fruiting inflorescences were obtained by hydrodistillation and analyzed by GC-MS. The essential oils were dominated by monoterpene hydrocarbons, mainly α-pinene (15.9-80.4%), myrcene (1.3-45.1%), (Z)-β-ocimene (0-14.3%), and α-phellandrene (0.40-19.7%). Bornyl acetate was the principal oxygenated monoterpene (up to 4.8%). Among sesquiterpene hydrocarbons, bicyclogermacrene (up to 2.4%) and germacrene D (up to 2.1%) were the most abundant, whereas oxygenated sesquiterpenes were represented mainly by (E)-nerolidol (0.1-7.1%). The diterpenes m-camphorene and p-camphorene were detected only in the leaves essential oil. Antibacterial activity was evaluated against Staphylococcus aureus NCTC 6571, Escherichia coli MG1655, and Pseudomonas aeruginosa PAO1. The inflorescence and fruiting-inflorescence oils showed the greatest activity against S. aureus (MIC and MBC = 5.3 mg/mL), whereas the leaf oil was less active (MIC and MBC = 10 mg/mL), and the root oil was inactive at the highest concentration tested (MIC > 20 mg/mL). No inhibition was detected against E. coli or P. aeruginosa, although changes in P. aeruginosa pigmentation were observed at 5.3-10 mg/mL. Growth-kinetics assays confirmed sustained inhibition of S. aureus by the inflorescence oil at 5.3 mg/mL over 24 h. In contrast, the oils did not significantly inhibit P. aeruginosa biofilm formation. These findings provide the first chemical profile of P. falcata essential oils and indicate activity varied among oils obtained from different organs, mainly against Gram-positive bacteria.