Synergistic interaction of phenylpropanoids with antibiotics against bacteria

Phenylpropanoids constitute a large part of our daily diet and there is a possibility that they might interact with synthetic drugs The present work was aimed at studying the interaction of seven phenylpropanoids (cinnamic, p-coumaric, caffeic, chlorogenic, ferulic, 3,4-dimethoxycinnamic and 2,4,5-trimethoxycinnamic acid) with five antibiotics (amikacin, ampicillin, ciprofloxacin, erythromycin and vancomycin) against Gram-negative (Escherichia coli, Enterobacter aerogenes and Pseudomonas aeruginosa) and Gram-positive (Staphylococcus aureus) bacteria The interaction studies were performed by chequerboard and time kill curve assays Both assays revealed that cinnamic, p-coumaric and ferulic acids were the most active They combined synergistically with the majority of the antibiotics and exhibited enhanced activity against all the micro-organisms The time kill curve parameters were better (P<0 05) for the combinations of amikacin with ferulic, cinnamic or p-coumaric acid than for the individual treatments Amikacin was the most favourable antibiotic and S aureus was the most sensitive microbe to most of the combinations These phenylpropanoids damaged the bacterial membrane as assessed by the LIVE/DEAD BacLight kit, and structure activity relationship studies indicated that hydrophilic groups enhanced this activity