Antibacterial Activity of Three Essential-oil-loaded Nanoemulsions Against Six Pathogenic Bacterial Strains

Finding antibiotic substitutes through ecological synthesis methods based on natural compounds is becoming a necessity for the treatment and prevention of microbial infections. In the present study, three essential-oil-loaded nanoemulsions (NEs) were prepared using the high-energy method. The obtained oil-in-water emulsions were characterized by determining the droplet size, PDI, zeta potential, and transmittance. Their stability against thermodynamic conditions and conservation was also investigated. Subsequently, the NE's antibacterial activities were assessed against Gram-positive (Staphylococcus aureus, Enterococcus faecalis, Listeria monocytogenes) and Gram-negative (Salmonella typhimurium, Escherichia coli, Pseudomonas aeruginosa) pathogenic bacterial strains. Our results revealed that NEs were successfully formed, with mean sizes ranging from 13.12 to 24.74 nm, confirming the nanometric size of the droplets. PDI values ranged from 0.278 to 0.317 and the percentages of transmittance exceeded 96.40%, indicating the optical clarity of the formulation. The thermodynamic stability study revealed a homogeneous size dispersion of the prepared NE1 and NE2, confirming their stabilities. Regarding NE3, an instability to centrifugal forces was registered, with phase separation observed, suggesting a heterogeneous dispersion of this preparation. The results of the antibacterial activity revealed that all tested NEs exerted a bactericidal effect against the majority of the tested strains (5 out of 6). However, a bacteriostatic effect by the tested substances against the E. coli strain was registered. NE3 exhibited the highest effect with MIC values ranging between 6.25 and 25% (v/v). The obtained NEs remain an efficient natural tool to fight against pathogenic bacteria and could be valorized as a potent drug delivery system.