Inhibiting Stenotrophomonas maltophilia, a Pathogenic Bacterium Responsible for Kernel Rot Disease in Pili nut (Canarium ovatum Engl.) with Ionic Liquid-loaded Nanoemulsions

Abstract

Pili nut production in the Philippines has grown steadily, but it faces significant challenges from pests and diseases, notably kernel rot. Yield losses due to this pathogen are still not measured, but the damage could extend from the purple immature to the dried postharvest nuts. Therefore, there is a pressing need for safe, effective, and environmentally friendly control measures. This study reports on the successful formulation of various Ionic Liquid-loaded Eucalyptus Essential Oil Nanoemulsions (IL-EEONE) for potential applications against Stenotrophomonas maltophilia, a pathogenic bacterium responsible for kernel rot disease in Pili nut (Canarium ovatum). Combining eucalyptus essential oil (EO) and Tween 80 in an oil-in-water (O/W) system, followed by stirring and sonication, and the subsequent loading of 1-Butyl-3-methylimidazolium hydrogen sulfate ([Bmim][HSO4]), an ionic liquid, at varying ratios (1:1, 2:1, and 3:1), yielding the formation of IL-EEONE. The nanoemulsion droplets exhibited a size range of 9.4–12.26 nm, highlighting their nanoscale dimensions. The IL-loaded nanoemulsions formulated at varying ratios typically displayed nearly monodisperse characteristics, except for the higher concentration 1:1 ratio of IL:EEONE formulation, as indicated by their Polydispersity Index (PDI) values. Fourier Transform Infrared (FT-IR) analysis further confirmed the successful formulation of the different IL-EEONE nanoemulsion compositions. Significantly, these nanoemulsions demonstrated excellent inhibitory properties against S. maltophilia, as indicated by Zone of Inhibition (ZOI) ranging from 11.3 ± 0.58 mm to 32.7 ± 0.58 mm. The antibacterial activity varied from partially active to very active across different formulations, with the 1:1 IL-EEONE ratio formulation standing out as exceptionally effective. This study shows the potential of IL-loaded nanoemulsions, IL-EEONE, as a potential agent for mitigating S. maltophilia causing the kernel rot disease, offering innovative avenues for addressing bacterial infection in agricultural settings.