Antibacterial Activity of Eucalyptus Essential Oils in Both Culture Media and Coated Materials

Different factors, including microbial resistance, have led to food contamination and increased human intoxication risks. Therefore, finding new adequate methods to fight against bacterial development is of interest. This study investigates the efficiency of eucalyptus essential oils to inhibit the growth of <i>Escherichia coli</i>, <i>Klebsiella pneumoniae</i>, <i>Listeria innocua</i>, <i>Salmonella typhimurium</i>, <i>Staphylococcus aureus,</i> and <i>Streptococcus pyogenes.</i> Oils were extracted from eucalyptus leaves by hydrodistillation and chemically analyzed on a coupled gas chromatography-mass spectrometer. The antibacterial activity was assessed in both culture media and film models. Results indicated that eucalyptus oils were rich in different chemicals including <i>α</i>-pinene in oils from <i>E. obliqua</i> (89.3%), <i>E. grandis</i> (39.9%), and <i>E. microcoris</i> (29.6%); p-cymene in <i>E. camaldulensis</i> (40.1%) and <i>E. grandis</i> (25.8%); and eucalyptol in <i>E. viminalis</i> (88.3%), <i>E. crebra</i> (84.6%), <i>E. polyanthemus</i> (80.7%), <i>E. melliodora</i> (78%), <i>E. maiden</i> (74.8%), and <i>E. globulus</i> (70.4%) oils. Terpinen-4-ol was found in <i>E. anceps</i> (5.7%) and <i>E. camaldulensis</i> (5.6%) while oils from <i>E. anceps</i> contained <i>β</i>-phellandrene (4.7%), cis- and trans-piperitols (6.5%), (cis)-p-(2 menthen)-1-ol (8.3%), geraniol (19.9%), and piperitone (10.5%). In comparison with a known antibiotic, azithromycin, essential oils from <i>E. grandis</i> and <i>E. anceps</i> exhibited significant antimicrobial efficacy against the growth of all tested microorganisms. The antibacterial efficiency from these oils was found to be higher than other essential oils tested (<i>p</i> < 0.05), with minimum inhibitory concentration and minimum bactericidal concentration ranging from 0.5 to 7 and 2.5 to 20 <i>μ</i>L/mL, respectively. Yet, at all concentrations tested (5-15 <i>μ</i>L/mL), hydroxy-propyl cellulose (HPC) films containing these oils indicated significant inhibition efficacy of the growth of bacteria compared to HPC films (<i>p</i> < 0.001). Further study on <i>E. grandis</i> and <i>E. anceps</i> oils is needed for their various valorization.