Evaluation of Antimicrobial Activity of Eucalyptus camaldulensis Essential Oil Against the Growth of Drug-Resistant Bacteria

Background: Due to the increasing resistance of pathogenic bacteria to common antibiotics, researchers are seeking alternative antimicrobial agents with plant origins. Objectives: The purpose of this study was to evaluate the activity of essential oil, extracted from the leaves of Eucalyptus camaldulensis, the major Eucalyptus species cultivated in Khuzestan, South of Iran, against the growth of drug-resistant bacteria. Methods: Essential oil was extracted from the leaves using the hydrodistillation method in a Clevenger apparatus. The constituents of the essential oil were determined by gas chromatography-mass spectrometry (GC-MS). Moreover, the antimicrobial activity of essential oil was assayed using the disk diffusion method. Theminimuminhibitory concentration (MIC) andminimumbactericidal concentration (MBC) were also determined using the macrodilution method. Results: Isolation and identification of the main components of essential oil identified 1,8-cineole (55.2%) as the main component. The essential oil could control resistant pathogenic bacteria. The greatest effect of essential oil was reported against Klebsiella pneumoniae with an inhibition zone diameter of 35 mm and MIC and MBC of 500 and 1500 ppm, respectively. On the other hand, the lowest effect was reported against Salmonella infantis and Salmonella enteritidis with an inhibition zone diameter of 11mmand MIC and MBC of 6,000 and 8,000 ppm, respectively. Conclusions: The essential oil of E. camaldulensis (Myrtaceae family) grown in Iran exhibited significant activities against some Gram-positive and Gram-negative bacteria. Therefore, E. camaldulensis is an effective antibacterial and bactericidal agent in the treatment of infectious diseases.