Enhancing Antibacterial Properties: Thymus daenensis Oil in Nanostructured Delivery Systems Versus Traditional Form

Today, the use of medicinal plants such as T. daenensis as a complementary and effective treatment method to control and inhibit the growth of pathogenic microorganisms is increasing all over the world. This study aimed to investigate the antimicrobial effects of T. daenensis essential oil (EO) and its nanocapsulated against some pathogenic bacteria isolated from aquatic and food samples.

In this experimental research, T. daenensis was collected in June 2023 in Shahrekord City. The EO of the dried aerial part of the plant was obtained by using a Clevenger device (steam distillation). The components in the EO were identified by gas chromatography-mass spectrometry (GC-Mass). T. daenensis EO nanocapsules were prepared using Tween 20, Tween 80 as emulsifier, polyethylene glycol as a co-solvent, acidic chitosan solution (1%), and modified starch (5%) as a coating. Transmission electron microscope (TEM) and dynamic light scattering (DLS) were used to confirm their structure. Antimicrobial properties against Listeria monocytogenes, Escherichia coli, Bacillus cereus, Salmonella typhimurium, Proteus mirabilis, Staphylococcus aureus and Klebsiella pneumoniae isolated from aquatic samples (fish and lobster) and various foods (raw milk, traditional ice cream and mutton, beef, chicken) were investigated by disc diffusion method, determination of minimum inhibitory concentration (MIC) and bactericidal (MBC) by microdilution method. Also, the prevention of biofilm formation was investigated.

The main components of the T. daenensis EO were thymol (75.31 percent), 8 p-Cymene (4.62 percent), carvacrol (4.2 percent), trans-cayophyllene (3.01 percent), terpenine (2.01 percent) and beta- myrcin (1.21 percent), respectively. TEM and DLS methods confirmed the structure of the T. daenensis EO nanocapsules. The size of nanocapsules was between 50 and 90 nm. The MIC amounts for the mentioned bacteria were between 62.5 and 250 μg/ml. The lowest MIC value for P. mirabilis, S. aureus, and K. pneumoniae was reported with a concentration of 62.5 μg/ml of T. daenensis EO nanocapsule. Also, the amounts of MBC for the mentioned bacteria were between 125 and 1000 µg/ml. According to the obtained results, the MIC and MBC levels for all mentioned bacteria against T. daenensis EO nanocapsule were lower than the EO alone (P<0.05). According to the results, with the increase in the concentration of EO, the diameter of the non-growth halo increased, while these results were not the same for T. daenensis EO nanocapsule. In all bacteria except S. aureus, the diameter of the non-growth halo for different concentrations of EO was greater than that of T. daenensis EO nanocapsule. The inhibition percentage of biofilm production was also reported 100% at 125 and 250 μg/ml of T. daenensis EO nanocapsule, except for K. pneumonia. In all concentrations of T. daenensis EO nanocapsule, the percentage of bacteria biofilm reduction was significantly higher than the EO alone (P<0.05).

Based on the findings of the study, the T. daenensis EO nanocapsule had more antibacterial properties than EO alone. It is suggested that future studies for the toxicology of T. daenensis EO nanocapsule on normal and cancerous cells be done iv-vitro. In addition, to apply it in the food industry, experimental studies on food models should also be conducted