Antimicrobial activity and toxicity of Eucalyptus globulus Labill. essential oil against vaginal microorganisms

The antimicrobial potential of commercial essential oil (EO) of Eucalyptus globulus L. was evaluated against six bacterial vaginal isolates (E. coli 1 and E. coli 2, S. aureus 1 and S. aureus 2, P. aeruginosa and P. mirabilis) and two isolates of Candida strains (C. albicans 1 and C. albicans 2). The antimicrobial activity was assessed through double-dilution micro-plate assay to determine the minimum inhibitory (MIC) and minimum bactericidal/fungicidal (МВС/ MFC) concentration. In addition, brine shrimp toxicity assay was performed in order to determine acute toxicity of the examined EO. The isolated strains of pathogens have shown strain specificity to the tested EO. Certain pathogens resistance was noticed toward the tested antibiotic, as well. E. coli isolates showed resistance to the tested antibiotics but did not show resistance against the Eucalyptus EO (E. coli 1 MIC/MBC 12.5/12.5 μL/mL; E. coli 2 MIC/ MBC 25/25 μL/mL). Moreover, the Eucalyptus EO showed effectiveness in application against S. aureus 2 (MIC/MBC 6.25/6.25 μL/mL), and C. albicans 1 strains (MIC/MFC 6.25/6.25 μL/mL). Furthermore, brine shrimp lethality bioassay revealed the Eucalyptus oil toxicity at an LC50 value of 2.66 mg/mL. The chemical composition of the separated essential oil was analyzed by gas chromatography combined with mass spectrometry (GC-MS) showing eucalyptol (59.63%), p-cymene (15.55%) and DL-limonene (14.90%) as dominant constituents. Although a number of toxicology trials are needed, these results provide scientific support to examination of Eucalyptus EO as an antimicrobial agent in alternative treatment of multiresistant human pathogens of vaginal origin.