Anti-Pseudomonas aeruginosa activity of hemlock (Conium maculatum, Apiaceae) essential oil

Conium maculatum, also known as ‘hemlock’ or ‘cicuta’, is a nitrophilous weed belonging to the Apiaceae family and occurring in hedgerows, pastures, waste ground, along rivers and roadsides. The notoriety of hemlock is linked to its historical use as poisoning, due to the content of piperidine alkaloids. On the other hand, little is known on the chemistry and bioactivity of other secondary metabolites occurring in the plant. In the present work, we have analysed the chemical composition and antimicrobial activity of the essential oils hydrodistilled from leaves and inflorescenes of C. maculatum growing in Sicily, Italy. The composition of essential oils was achieved by gas chromatography-mass spectrometry (GC-MS) analysis, whereas the inhibitory effects on the growth of two Gram negative strains, namely Escherichia coli and Pseudomonas aeruginosa were assessed by two different analysis. The essential oils exhibited different chemical profiles, with that of flowers being characterized by the piperidine alkaloid 1-butylpiperidine (26.4%) and myrcene (24.0%), whereas the leaf essential oil was mainly composed of sesquiterpenes hydrocarbons (64.2%) among which (E)-caryophyllene (54.8%) was the predominant component. The latter oil was particularly active in inhibiting the growth of P. aeruginosa, forming an inhibition halo comparable to the antibiotic colistin. These results shed light on the possible application of hemlock essential oils as antimicrobial agents.