Tea tree essential oil as a natural biocide: Chemical analysis and its efficacy against microbial, biofilm, and insect challenges

Abstract

Recent studies have demonstrated the potential of natural plant essential oils (EOs) as alternatives to chemical preservatives due to their notable antimicrobial activity, rapid biodegradability, and high safety profile. The aim of this study was to evaluate the chemical composition and biological activities of essential oil from Melaleuca alternifolia (tea tree). GC-MS analysis identified 31 volatile compounds, with γ-terpinene (25.3%) as the dominant component. Antioxidant activity was assessed using DPPH and ABTS assays, yielding IC₅₀ values of 28.07 mg/mL and 0.51 mg/mL, respectively. Antimicrobial efficacy was tested against twelve microorganisms using the disc diffusion method and determination of minimum inhibitory concentrations (MIC). The largest inhibition zones were observed against biofilm-forming Salmonella enterica (11.33 mm) and S. enterica (10.33 mm), with MIC₅₀ values ranging from 0.16 to 8.08 mg/mL. The highest in situ inhibition was recorded on the kiwi model against Yersinia enterocolitica (88.83%), on pear against Staphylococcus aureus, on parsley against Listeria monocytogenes, and on radish against biofilm-forming S. enterica all at the highest applied concentration of 500 µL/L. Anti-biofilm activity was evaluated using crystal violet staining and MALDI-TOF MS Biotyper spectral profiling. Spectral differences in MALDI-TOF MS profiles between planktonic and biofilm cells suggest that tea tree essential oil triggers distinct bacterial responses depending on physiological state and surface material. Insecticidal activity against adult Megabruchidius dorsalis yielded LC₅₀ and LC₉₀ values of 20.60% and 54.46%, respectively, with 100% mortality recorded at 100% essential oil concentration. These findings highlight the broad-spectrum bioactive potential of tea tree essential oil and its promise as a natural biocidal agent.