Species-specific antimicrobial activity of essential oils and enhancement by encapsulation in mesoporous silica nanoparticles

• Published in: Industrial crops and products 2018-10, Vol.122, p.582-590
• Main Authors: Bravo Cadena, Marimar, Preston, Gail M., Van der Hoorn, Renier A.L., Townley, Helen E., Thompson, Ian P.
• Format: Article
• Language: English
• Subjects: Antimicrobials; Bacterial phytopathogens; Crop protection; Essential oils; Mesoporous silica nanoparticles
• ISSN: 0926-6690; 1872-633X
• DOI: 10.1016/j.indcrop.2018.05.081

[Display omitted] •Forty one essential oils were evaluated against phytopathogenic bacteria.•Cinnamon and mustard essential oils inhibited bacterial growth at 0.016% (v/v).•Species-specific effect of oils: >67% showed specificity towards the pathogen.•Silica nanoparticle immobilisation increased cinnamaldehyde potency by 10-fold.•Cinnamaldehyde-nanoparticles eliminated up to 99.9% of bacterial growth. Essential oils are volatile plant compounds that are biologically active and play an important role in natural plant protection. There are currently ∼3000 essential oils known, of which over 300 are commercially important for a variety of industries. In fact, the essential oil global market has been estimated to reach 13.94 billion USD with a demand of over 370,000 tons by 2024. These compounds have a wide variety of applications in agriculture, food and beverage, cosmetics, medicine, amongst other industries. A promising application of essential oils is as antimicrobials to target the vast number of diseases affecting crops. However, their volatile nature limits their effective use as free agents. To overcome this, we have investigated the use of mesoporous silica nanoparticles to protect essential oils from evaporation and degradation and to enhance their antimicrobial activity against bacterial phytopathogens. Silica nanoparticles were used due to their potential to be produced at an industrial scale and their biocompatibility. As a proof of concept, we evaluated 41 essential oils against bacterial phytopathogen Pseudomonas syringae pv. pisi, causative agent of pea bacterial blight. Additionally, we compared the effect of such essential oils against Pectobacterium carotovorum subsp. carotovorum and Pseudomonas fluorescens. Two of the most effective antimicrobials, cinnamon (Cinnamomum zeylanicum) and mustard (Brassica nigra) oils, were able to inhibit bacterial growth after 24 h at a concentration as low as 0.016% (v/v). Besides efficacy, the species-specificity of essential oils was demonstrated with >67% of oils tested displaying specificity towards pathogenic P. syringae pv. pisi over non-pathogenic Pseudomonas fluorescens. Furthermore, the encapsulation of essential oils into mesoporous silica nanoparticles (MSNPs) as a means of extending and improving their antimicrobial effect was found to enable a 10-fold increase in potency compared to the free essential oil. Cinnamaldehyde immobilised onto MSNPs proved to be the most effective antimicrobial, elimi