Chemical Composition Analysis of Tea Tree Oil and Its Antibacterial Activity Against Pathogenic Bacteria of Skin Ulceration Syndrome in Apostichopus japonicus

In order to study the chemical constituents of tea tree essential oil (TTO) and its antibacterial activity against the pathogens causing skin ulceration syndrome in Apostichopus japonicus, the chemical constituents of several TTO batches were analyzed and relatively quantified by using the gas chromatography–mass spectrometry (GC-MS) coupled with the peak area normalization method. A batch with high content of active components was selected for the antibacterial tests of biological bacteriostatic agent against the pathogens. The results indicated that the TTO from Beihai, Guangxi (Batch No. 20230503) exhibited the highest total content of active components (89.17%), including terpinen-4-ol (38.44%), γ-terpinene (21.32%), 1,8-cineole (1.31%), α-terpinene (11.63%), and α-pinene (3.01%). Consequently, this batch was chosen for the subsequent antibacterial study. In the disk diffusion assay, the inhibition zone diameters of tea tree essential oil against Vibrio harveyi, Vibrio alginolyticus, and Pseudoalteromonas sp. were 36.50 ± 3.2 mm, 26.36 ± 1.2 mm, and 31.85 ± 4.0 mm, respectively. The minimum inhibitory concentrations (MICs) of the TTO-based biological inhibitors against Vibrio harveyi, Vibrio alginolyticus and Pseudoalteromonas sp. were 30, 40 and 30 mg/mL, respectively, while the minimum bactericidal concentrations (MBCs) were 20, 20 and 15 mg·mL⁻¹, respectively. In the safety assessment on Apostichopus japonicus, the concentration of tea tree essential oil below 100 mg·mL⁻¹ had no effect on the growth of Apostichopus japonicus, and no chemical residues were detected, indicating that it had certain safety and good bacteriostatic effect.