PSIII-3 Investigating the antibacterial properties of terpene and phenylpropanoid based essential oil blends against Escherichia coli.

Abstract A key strategy within the One-Health framework to combat antibiotic-resistant bacteria is the development of new, effective and sustainable antimicrobials with a particular focus on natural products such as essential oils to combat antimicrobial resistance (AMR) in dairy cattle. This study investigated antibacterial potential of two essential oil blends (EOBs) on Escherichia coli O157:H7 Strain Sakai DNA, Complete genome (E. coli): Terpene based essential oil blend (EOB-T) containing equal proportions of eucalyptus, thyme, juniper and oregano (2.5:2.5:2.5:2.5) and phenylpropanoid-based essential oil blend (EOB-P) containing clove, cinnamon bark, anise and nutmeg (2.5:2.5:2.5:2.5). Using an adapted broth microdilution method, minimum inhibitory concentrations (MICs) and 24 h growth assays were conducted to assess the effects of these essential oil blends across a gradient of concentrations (0.1%, 0.2%,0.4%, 0.8%, 1.56%, 3.125%, 6.25%, 12.5%, 25%, 50%). This was a dose-response study using a Completely Randomized Design (CRD) in a controlled laboratory setting. Data were analyzed using One-way ANOVA, followed by Dunnett’s multiple comparison test. Growth curves were generated using GraphPad Prism. For both EOBs, the lag phase finished within the first 2-3 hours at the lower concentrations. Bacteria growth was completely inhibited at 50% concentration (P< 0.001) for EOB-P while completion inhibition of growth was observed at 6.25% concentration of EOB-T (P< 0.001). Bacteria at the sub-MIC concentrations for both EOBs was significantly reduced compared to the untreated control (P < 0.001). These findings suggest that both EOB-T and EOB-P exhibited strong antimicrobial activity against E. coli and could serve as a natural alternative to synthetic antimicrobials in livestock health management.