Antimicrobial activity of lavender oil against gram-negative bacteria

Abstract

Introduction. Synthetic antimicrobials and antibiotics have long been used to treat infections in humans and animals. However, the increasing antimicrobial resistance has reduced their effectiveness. Consequently, recent research has turned toward natural alternatives, particularly those derived from plants. Plants and their extracts have been used in traditional medicine for centuries. Essential oils, volatile secondary metabolites from plants, are commonly applied in aromatherapy, cosmetics, and medicine. Various essential oils, such as those from thyme, oregano, mint, cinnamon, cumin, sage, clove, and eucalyptus, have demonstrated strong antimicrobial activity. Purpose of the study. This study aimed to evaluate the antimicrobial activity of lavender essential oil (EOL) against Gram-negative bacterial strains. Material and methods. The EOL used in this study was extracted from the flowers of Lavandula angustifolia cultivated in the Republic of Moldova. The antibacterial activity was tested against Gram-negative bacterial strains from the American Type Culture Collection (ATCC), including Escherichia coli ATCC 25922, Pseudomonas aeruginosa ATCC 27853, Salmonella Enteritidis ATCC 13076 and Acinetobacter baumannii ATCC BAA-747. The antimicrobial effect was determined using the disc diffusion method. Oxytetracycline (20 μg) was used as positive control and methanol was used as the negative control. The minimum inhibitory concentration (MIC) was determined for the same bacterial strains using the microtiter broth dilution method. Results. Based on the results of the disk diffusion test, the EOL exhibited a remarkable antimicrobial effect against all tested bacterial species, except Pseudomonas aeruginosa, which demonstrated resistance even at the highest concentration of EOL. The strongest antibacterial activity was observed at the 1:1 dilution for the majority of the tested strains. The largest inhibition zone was recorded for Salmonella Enteritidis, measuring 24 mm in diameter. Both Acinetobacter baumannii and S. Enteritidis remained sensitive even at the 1:10 dilution, indicating a notable susceptibility to EOL. Analysis of the MIC results for EOL against Gram-negative bacteria revealed that most strains exhibited similar MIC values, ranging between 0.5% and 1%, with the exception of P. aeruginosa. All P. aeruginosa strains showed high resistance, with MIC values exceeding 2%. The MIC was determined to be 0.5% for Escherichia coli and Salmonella Enteritidis, while for Acinetobacter baumannii, the MIC was 1%. Conclusions. Based on the results, it can be concluded that EOL is effective against most Gram-negative bacteria, suggesting its potential as a promising alternative for controlling infections caused by these pathogens.