Essential oils from Eucalyptus camaldulensis, Mentha piperita L., and Rosmarinus officinalis L.: a new frontier in combating antibiotic-resistant E. coli by inducing cellular components release.

Escherichia coli biofilms, a major cause of persistent infections, often exhibit resistance to conventional antibiotics. This study investigates the potential of essential oils derived from Eucalyptus camaldulensis, Mentha piperita L., and Rosmarinus officinalis L. as natural alternatives to combat these infections. A comparative analysis of biofilm quantification was done by using 0.5% crystal violet and safranin. The essential oils, characterized by Fourier Transform Infrared Spectroscopy and Gas Chromatography-Mass Spectrometry, demonstrated significant antibacterial activity against diverse Escherichia coli strains, with Minimum Inhibitory Concentration and Minimum Bactericidal Concentration values ranging from 3.13 to 35 µg/mL. Gas Chromatography-Mass Spectrometry revealed the presence of 1,8 cineol (90%) in the essential oils from Eucalyptus camaldulensis, mono terpenoids (64%) in the essential oils from Mentha piperita L and D1-2- ethylhexyl chloroformate (94%) in the essential oils from Rosmarinus officinalis L as major components. The essential oils effectively inhibited biofilm formation by 55-96% and eradicated existing biofilms by 57.5-95%. Mechanistic studies revealed that the essential oils induced the release of cellular components, suggesting a novel mode of action. These findings highlight the potential of these oils as promising agents for combating Escherichia coli infections, particularly those caused by biofilm-forming strains. Further research is warranted to optimize this approach for clinical applications and to fully elucidate their mechanisms of action.