Synergistic effect of fennel essential oil and hydrogen peroxide on bacterial biofilm

Introduction
Staphylococcal biofilm formation significantly challenges wound management. The causes of difficult-to-treat wounds are not only methicillin-resistant staphylococci, but also methicillin-sensitive strains with different patterns of resistance. Bacterial biofilm significantly limits the access and activity of antimicrobials used in dermatological infections.

Aim
To evaluate the synergistic effect of fennel essential oil (FEO) and H2O2 on biofilm formation by Staphylococcus aureus (MSSA and MRSA) reference strains.

Material and methods
Minimum inhibitory concentration (MIC) values were determined for FEO and H2O2 against S. aureus reference strains by the broth microdilution method. The combined effects of the FEO and H2O2 were calculated and expressed in terms of a fractional inhibitory concentration index (FICI) using the checkerboard method. The FEO composition was analyzed by the GC-MS method. The data were analysed by one-way ANOVA.

Results
Decreased MIC values for FEO combined with H2O2 were observed in comparison to FEO itself. The combinations of FEO and H2O2 determined synergistic effects on all S. aureus reference strains. Subinhibitory concentration of FEO alone and in combination with 0.5 MIC of H2O2 significantly decreased the production of biofilm biomass in S. aureus strains and reduced the metabolic activity of attached cells.

Conclusions
Combination of fennel essential oil containing nearly 80% trans-anethole and H2O2 represents a potential for further basic and applied research on wound management.