Synergistic effects of cinnamaldehyde and cinnamic acid in cinnamon essential oil against S. pullorum

Cinnamon is an important spice crop that is widely cultivated in tropical regions. In this study, the antibacterial activities of four accessions of cinnamon essential oil (CEO) belonging to three different species (CEO1 and CEO4, Cinnamomum cassia Presl. (Lauraceae) bark; CEO2, Cinnamomum zeylanicum Blume (Lauraceae) bark; CEO3, Cinnamomum burmannii Blume (Lauraceae) bark) toward Salmonella enterica subsp. enterica serovar pullorum (S. pullorum) were evaluated by microdilution assay and kinetic analysis. The minimum inhibitory concentration (MIC) of the CEOs were all 0.31 mg/mL, and kinetic analysis suggested that the lag phase and maximum specific growth rate of bacteria were concentration dependent. Furthermore, to explore the synergistic antibacterial effects between main components and minor components, the volatile constituents of CEOs were determined by gas chromatography-mass spectrometry (GC-MS). Cinnamaldehyde (CM) (57.73 %-91.79 %) was the principal constituent in CEO1-CEO4 (p < 0.05), with CEO3 having the highest CM contents. Screening of the active minor compounds isolated from CEOs showed that cinnamic acid (CA), salicylaldehyde, alpha-pinene, o-anisaldehyde with MIC value of 0.31-2.5 mg/mL had better antibacterial activity. A synergistic effect against S. pullorum was observed when CA was combined with CM. To explore the potential synergistic mechanism, the membrane glycerophospholipid (GPL) composition of S. pullorum was characterized by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). CM, CA, and their combination regulated the levels of most phosphatidylethanolamines (PEs), phosphatidylglycerols (PGs), phosphatidic acids (PAs), and some cardiolipins (CLs).

Automated summary

This study evaluated the antibacterial activities of different types of cinnamon essential oils against Salmonella enterica and explored the synergistic effects between main components and minor components. The results showed that cinnamaldehyde was the principal constituent in cinnamon essential oils, while minor compounds like cinnamic acid exhibited good antibacterial activity. The combination of cinnamaldehyde and cinnamic acid showed a synergistic effect against Salmonella enterica. Additionally, the membrane glycerophospholipid composition of Salmonella enterica was regulated by cinnamaldehyde, cinnamic acid, and their combination.