Antibacterial activity of free or encapsulated selected phenylpropanoids against Escherichia coli and Staphylococcus epidermidis

Aims Antibacterial activities of phenylpropenes (PPs) (eugenol, isoeugenol, estragole and trans-anethole) and hydroxycinnamic acids (HCAs) (p-coumaric, caffeic and ferulic acids) were assessed against Escherichia coli and Staphylococcus epidermidis. Effect of cyclodextrin and liposome encapsulation on the PPs activity was also evaluated. Methods and Results All PPs inhibited the bacterial growth in the hundred micromolar range, while HCAs did not, as determined by broth macrodilution. Anethole and estragole showed a higher efficiency than eugenol and isoeugenol, and E. coli was more susceptible than S. epidermidis. Hydroxypropyl-beta-cyclodextrin/PP complexes and anethole-loaded Lipoid S100-liposomes were prepared by freeze-drying and ethanol injection respectively. Both formulations were substantially less active than free PPs. For instance, E. coli growth inhibition was about 14% for all HP-beta-CD/PP complexes evaluated at MIC50 values of free PPs (P < 0 center dot 05), and about 12% for liposomal anethole evaluated at minimal bactericidal concentration value of free anethole (P < 0 center dot 05). Conclusions Hydrophobicity appears to be crucial for PPs antibacterial activity. Encapsulation in cyclodextrin and liposome seems to retain the PPs preventing their interaction with bacteria. Significance and Impact of the Study This study highlights the structural features of simple phenylpropanoids related to their antibacterial activity. The limitations of conventional encapsulation systems on the activity of PPs should be considered in future applications.