Antimicrobial synergism and antagonism of salicylaldehyde in Filipendula vulgaris essential oil

The leaf essential oil of Filipendula vulgaris, consisting mainly of salicylaldehyde (68.6%), was screened for its antimicrobial activity by the disk diffusion and microdilution broth assays. The essential oil remarkably inhibited the growth of all of the tested bacteria and fungi. It seems that the antimicrobial nature of F. vulgaris essential oil can be attributed to the synergistic interactions of the compounds constituting the oil rather than to the presence of a single inhibitory agent. A synergy in salicylaldehyde/linalool mixtures was observed with a maximum interaction situated in the range between 60:40 and 80:20 (mol ratio). At this concentration range (at a dose of 1.7 μg/disk) no microbial growth was observed while the respective pure compounds, at the corresponding quantities, are shown to be dramatically less active. The MIC value for the 60:40 mixture was determined to be less that 0.009 mg/ml. In addition, an antagonistic relationship between salicylaldehyde and methyl salicylate was established. The maximum (negative) interaction was shown to correspond approximately to the mixture at the 40:60 (methyl salicylate/salicylaldehyde) mol ratio resulting in the complete loss of activity at the investigated dose.