Study on the mechanisms of the antibacterial action of some plant alpha,beta-unsaturated aldehydes

Aims: In this paper the mechanisms involved in the antibacterial effect of six 2E-alkenals [(E)-2-hexenal, (E)-2-eptenal, (E)-2-octenal, (E)-2-nonenal, (E)-2-decenal and (E,E)-2,4-decadienal] were investigated. Methods and Results: We measured the release of carboxyfluorescein (CF) trapped in liposomes of phosphatidylcholine (PC) following exposure to the aldehydes mentioned above, in comparison with that elicited by hexanal and nonanal; the modifications of the thermotropic behaviour of liposomes of dimyristoylphosphatidylcholine (DMPC) induced by (E,E)-2,4-decadienal (the aldehyde endowed with the highest microbicidal activity) were evaluated by means of differential scanning calorimetry. With the exception of hexanal, all aldehydes tested caused rapid CF leakage from PC liposomes. The effectiveness order correlates well with the chain length and the presence of the α,β-double bond. Furthermore (E,E)-2,4-decadienal is able to interact with and cross DMPC bilayers. Conclusions: The present findings suggest that the 2E-alkenals tested elicit, very likely, a gross perturbation of the lipidic fraction of plasmatic membranes and are able to penetrate into bacterial cells. Significance and Impact of the Study: These data represent an interesting background for a rational employment of the plant 2E-alkenals tested as antimicrobial agents.