Possible mode of synergistic antimicrobial action of essential oil components cinnamaldehyde and eugenol in combination against foodborne bacteria Listeria monocytogenes and Salmonella typhimurium

Synergistic antimicrobial interaction is a promising strategy to overcome the challenges of microbial contamination in food. The aim of this study was to elucidate possible mode of synergistic antimicrobial interaction of essential oil components cinnamaldehyde and eugenol in combination against foodborne bacteria Listeria monocytogenes and Salmonella typhimurium using standard methods. At their individual effect, eugenol at 0.5×MIC concentration acted upon bacterial cell envelope leading to membrane damage and cytoplasm leakage whereas cinnamaldehyde at 0.5×MIC concentration failed to do so. But in combination, at their 0.5×MIC concentrations, eugenol allows cinnamaldehyde to enter inside the bacterial cells of studied bacterial pathogens with ease. Once they entered inside the cell, both eugenol and cinnamaldehyde simultaneously induced a significant disturbance in the cytoplasm of bacterial cells leading to significant release of cellular materials compared to their individual effects due to their synergistic interaction. The ultimate result is the loss of membrane integrity which caused a significant change in cellular morphology and subsequently led to cell lysis and cell death. The results provide evidence that eugenol/cinnamaldehyde blend at sufficiently low concentration may serve as a more potent natural alternative to synthetic antimicrobial food preservatives in food industry. This study can provide an interesting platform in the near future for this area of research. To the best of our knowledge this paper is the first to study possible mode of synergistic antimicrobial interactions of essential oil components in combination against foodborne Gram-positive and Gram-negative bacteria.