Comparative study of volatile oil constituents, anti-microbial properties, and antibiofilm activities in Eucalyptus camaldulensis and Eucalyptus globulus: insights from central Saudi Arabia

Eucalyptus is a fragrant plant with a highly volatile oil content grown worldwide. This study investigated the phytochemical and biological features of two Eucalyptus species, E. camaldulensis and E. globulus, cultivated in Central Saudi Arabia. Phytochemical analysis revealed 17 compounds in E. camaldulensis and 13 in E. globulus, with α-pinene and 1,8-cineole being both plants’ most abundant volatile components. The antimicrobial activity revealed that Salmonella typhimurium ATCC 13311 and Candida albicans ATCC 10231 are the most susceptible to E. camaldulensis, with the zone of inhibition diameters (ZIDs) of 17.0 ± 0.2 mm and 22.0 ± 0.3 mm, respectively. In contrast, for E. globulus, methicillin-resistant Staphylococcus aureus and Candida albicans ATCC 10231 were the most susceptible, with ZIDs of 13.0 ± 0.2 mm and 20.0 ± 0.2 mm, respectively. E. camaldulensis had minimum inhibitory concentration (MIC) range from 1.56 to 12.5 μL/mL, minimum biocidal concentration (MBC) range from 3.125 to 25.0 μL/mL, minimum biofilm inhibitory concentration (MBIC) range from 3.125 to 25.0 μL/mL, and minimum biofilm eradication concentration (MBEC) from 6.25 to 50.0 μL/mL, while E. globulus had MIC range from 3.125 to 12.5 μL/mL, MBC range from 6.25 to 25.0 μL/mL, MBIC range from 6.25 to 25.0 μL/mL, and MBEC range from 12.5 to 50.0 μL/mL, for the tested organisms. E. camaldulensis demonstrated better antimicrobial activity than E. globulus against the tested organisms, making it a promising antimicrobial drug candidate. Further research is required to determine its effectiveness in treating different human infections.

桉树（Eucalyptus）是一类香气浓郁且挥发油含量极高的植物，在全球范围内广泛种植。本研究针对沙特阿拉伯中部种植的两种桉树——赤桉（E. camaldulensis）和蓝桉（E. globulus）的植物化学特性与生物学特性展开了探究。植物化学分析结果显示，赤桉中检出17种化合物，蓝桉中检出13种；α-蒎烯（α-pinene）与1,8-桉叶素（1,8-cineole）均为两种桉树含量最高的挥发性成分。抗菌活性实验结果表明，鼠伤寒沙门氏菌（Salmonella typhimurium）ATCC 13311与白色念珠菌（Candida albicans）ATCC 10231对赤桉提取物最为敏感，其抑菌圈直径（zone of inhibition diameters, ZIDs）分别为17.0 ± 0.2 mm与22.0 ± 0.3 mm。与之相对，蓝桉对耐甲氧西林金黄色葡萄球菌（methicillin-resistant Staphylococcus aureus）与白色念珠菌ATCC 10231的抑制效果最佳，对应的抑菌圈直径分别为13.0 ± 0.2 mm与20.0 ± 0.2 mm。针对本次实验所用受试菌株，赤桉的最低抑菌浓度（minimum inhibitory concentration, MIC）范围为1.56~12.5 μL/mL，最低杀菌浓度（minimum biocidal concentration, MBC）范围为3.125~25.0 μL/mL，最低生物膜抑制浓度（minimum biofilm inhibitory concentration, MBIC）范围为3.125~25.0 μL/mL，最低生物膜清除浓度（minimum biofilm eradication concentration, MBEC）范围为6.25~50.0 μL/mL；而蓝桉的MIC范围为3.125~12.5 μL/mL，MBC范围为6.25~25.0 μL/mL，MBIC范围为6.25~25.0 μL/mL，MBEC范围为12.5~50.0 μL/mL。相较于蓝桉，赤桉对受试菌株展现出更优异的抗菌活性，是极具潜力的抗菌药物候选对象。后续仍需开展进一步研究，以明确其在治疗各类人类感染性疾病中的实际疗效。