Volatile terpenes represent the largest group of Cannabis sativa L. components and they are responsible for its aromatic properties. Even if many studies on C. sativa have been focused on cannabinoids, which are terpenophenolics, little research has been carried out on its volatile terpenic compounds. In the light of all the above, the present work was aimed at the chemical characterization of seventeen essential oils from different fibre-type varieties of C. sativa (industrial hemp or hemp) by means of GC-MS and GC-FID techniques. In total, 71 compounds were identified, and the semi-quantitative analysis revealed that α- and β-pinene, β-myrcene and β-caryophyllene are the major components in all the essential oils analysed. In addition, a GC-MS method was developed here for the first time, and it was applied to quantify cannabinoids in the essential oils. The antibacterial activity of hemp essential oils against some pathogenic and spoilage microorganisms isolated from food and food processing environment was also determined. The inhibitory effects of the essential oils were evaluated by both the agar well diffusion assay and the minimum inhibitory concentration (MIC) evaluation. By using the agar diffusion method and considering the zone of inhibition, it was possible to preliminarily verify the inhibitory activity on most of the examined strains. The results showed a good antibacterial activity of six hemp essential oils against the Gram-positive bacteria, thus suggesting that hemp essential oil can inhibit or reduce bacterial proliferation and it can be a valid support to reduce microorganism contamination, especially in the food processing field.

The emergence of antibiotic-resistant bacteria has become a major concern worldwide. This trend indicates the need for alternative agents to antibiotics, such as natural compounds of plant origin. Using agar disc diffusion and minimum inhibitory concentration (MIC) assays, we investigated the antimicrobial activity of Citrus aurantium (AEO), Citrus x limon (LEO), Eucalyptus globulus (EEO), Melaleuca alternifolia (TTO), and Cupressus sempervirens (CEO) essential oils (EOs) against three representatives of antibiotic-resistant pathogens and respective biofilms: vancomycin-resistant enterococci (VRE), methicillin-resistant Staphylococcus aureus (MRSA), and extended-spectrum β-lactamase (ESBL)-producing Escherichia coli. Using the checkerboard method, the efficacy of the EOs alone, in an association with each other, or in combination with the reference antibiotics was quantified by calculating fractional inhibitory concentrations (FICs). All the EOs displayed antibacterial activity against all strains to different extents, and TTO was the most effective. The results of the EO–EO associations and EO–antibiotic combinations clearly showed a synergistic outcome in most tests. Lastly, the effectiveness of EOs both alone and in association or combination against biofilm formed by the antibiotic-resistant strains was comparable to, and sometimes better than, that of the reference antibiotics. In conclusion, the combination of EOs and antibiotics represents a promising therapeutic strategy against antibiotic-resistant bacteria, even protected inside biofilms, which can allow decreasing the concentrations of antibiotics used.