Antimicrobial Activity and Mechanism of Action of Litsea cubeba Essential Oil against Cladosporium

In this study, essential oil was extracted from the fruit of Litsea cubeba by hydrodistillation, and its major components were analyzed by gas chromatography-mass spectrometry (GC-MS). The antimicrobial activity of the essential oil against Cladosporium was determined and its mechanism of action was explored by examining the antibacterial rate and mycelium inhibition rate of Cladosporium, the liposome leakage assay, and the determination of leakage of intracellular ions and macromolecular contents and ATPase activity. The results indicated that the major components of L. cubeba essential oil were terpenoids such as citral and monoterpene oxides. Its minimum inhibitory concentration against Cladosporium was 0.64% (V/V). The essential oil was effective in inhibiting the growth of Cladosporium mycelium and altering its molecular structure and functional groups. The initial target for the antimicrobial activity of the essential oil was the cell membrane, where it increased the permeability of the phospholipid bilayer in a concentration-dependent manner, leading to the leakage of fluorescein encapsulated in liposomes without collapsing the bilayer. It also caused the leakage of intracellular K+, Ca2+, and macromolecules, thereby inhibiting the growth and reproduction of Cladosporium. Scanning electron microscope observation further confirmed that L. cubeba essential oil disrupted the morphology of Cladosporium mycelium, resulting in severe loss of intracellular contents.