Antimicrobial and antibiofilm activity of the essential oil from dried leaves of Eucalyptus staigeriana

ABSTRACT: In recent years, compounds with biological properties produced by plants have received attention as an alternative to control microorganisms. Essential oils extracted from green leaves of Eucalyptus sp. have been demonstrated to have antimicrobial activities, but so far there are no reports of antimicrobial activity of essential oils extracted from dried leaves of Eucalyptus staigeriana. So, the objectives of this study were to determine the chemical composition of the essential oils obtained from dried leaves of E. staigeriana (EOdlES) and to evaluate in vitro antimicrobial and antibiofilm activities of EOdlES against gram-positive and gram-negative, resistance and multiresistant Enterococcus faecalis isolated from food and clinical samples. The characterization of EOdlES was performed by gas chromatography-mass spectrometry (GC/MS). For this study, 26 bacterial strains were used, which included 11 reference strains and 15 antibiotic resistant and multiresistant E. faecalis strains. Antimicrobial activities of EOdlES against gram-positive and gram-negative were determined using the disc diffusion method. The minimum inhibitory concentration (MIC) value was evaluated by a microbroth dilution technique. The antibiofilm effects were assessed by microtiter plate method. As a result, 21 compounds were identified, being oxygenated monoterpenes (69.58%) the major chemical family. EOdlES showed only antimicrobial activity against gram-positive strains. E. faecalis resistant and multiresistant strains show the lowest MIC (3.12 to 6.25%), when compared with reference E. faecalis strain. EOdlES has the ability to inhibit the biofilm formation, but little or none ability to inhibit the preformed biofilm. This study demonstrates that EOdlES is a promising alternative to control important foodborne and clinic gram-positive resistant bacteria.摘要：近年来，植物来源的具有生物活性的化合物作为微生物防控的替代方案受到广泛关注。已有研究证实，从桉树属植物（Eucalyptus sp.）绿叶中提取的精油具有抗菌活性，但截至目前，尚无关于斯塔格桉（Eucalyptus staigeriana）干燥叶片提取精油（EOdlES）的抗菌活性的相关报道。为此，本研究旨在明确斯塔格桉干燥叶片提取精油（EOdlES）的化学成分，并体外评估该精油对从食品及临床样本中分离得到的革兰氏阳性、革兰氏阴性、耐药及多重耐药粪肠球菌（Enterococcus faecalis）的抗菌与抗生物膜活性。 本研究采用气相色谱-质谱联用技术（GC/MS）对EOdlES进行成分表征。本次研究共使用26株细菌菌株，其中包含11株参考菌株与15株抗生素耐药及多重耐药粪肠球菌菌株。采用纸片扩散法测定EOdlES对革兰氏阳性及革兰氏阴性菌的抗菌活性；通过微量肉汤稀释法评估其最低抑菌浓度（MIC）；利用微孔板法检测其抗生物膜效应。 研究结果显示，本研究共鉴定出21种化合物，其中氧化型单萜类为主要化学成分家族，占比达69.58%。EOdlES仅对革兰氏阳性菌株表现出抗菌活性。相较于参考粪肠球菌菌株，耐药及多重耐药粪肠球菌菌株的MIC值最低（3.12%~6.25%）。EOdlES能够抑制生物膜的形成，但对已形成的生物膜几乎无抑制作用或仅具备极微弱的抑制能力。 本研究表明，EOdlES是一种极具潜力的替代方案，可用于防控重要的食源性及临床耐药革兰氏阳性细菌。