Investigations of Antimicrobial Activity of Eucalyptus Camaldulensis Extracts against Six Pathogenic Bacteria in Planktonic Form and Biofilm

Background & Aims: Microorganisms are protected from antimicrobial agents when placed in biofilm structure. Biofilm-producing microorganisms are responsible for many problems in industry and medicine; therefore, it is essential to find new techniques for removing and inhibiting biofilms. This study aimed to examine the antimicrobial effect of Eucalyptus camaldulensis alcoholic extracts against planktonic form and biofilm of six bacteria including Staphylococcusaureus aureus, Bacillus cereus, Streptococcus pneumoniae, Pseudomonas aeruginosa, Escherichia coli, and Klebsiella pneumoniae. Methods: Antimicrobial activities of the plant extracts against the planktonic form of bacteria were evaluated using disc diffusion method. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values were determined using a macrobroth dilution technique. Anti-biofilm effects were assessed using microtiter plate method. Results: The results of this study confirmed the strong ability of E. camaldulensis extracts against the biofilm of tested bacteria and their free-living forms. Ethanolic extracts were more effective in inhibiting planktonic bacterial growth than methanolic extracts. Anti-biofilm effects of plant extracts were associated with the solvent and extract concentration. Eucalyptus camaldulensis methanol extract of 20 mg/ml concentration was the most efficient in the inhibition of biofilm formation of Staphylococcus aureus (84.42%). These extracts had the ability to remove more than 50% of stabilized biofilms. In Klebsiella pneumonia, however, only a 29.20% eradication of biofilms was observed. The highest decrease in methabolic activity was observed in Streptococcus pneumoniae biofilms (82.13%) treated with 20 mg/ml ethanolic extract. Conclusion: In this study, the antimicrobial activity of Eucalyptus camaldulensis extracts against the selected microorganisms was demonstrated. Thus, these extracts are recommended as a suitable option against the selected isolates