Thymol is a monoterpene phenolic derivative extracted from the Thymus vulgaris which has antimicrobial effects. In the present study, thymol-loaded chitosan nanogels were prepared and their physicochemical properties were characterized. The encapsulation efficiency of thymol into chitosan and its stability were determined. The in vitro antimicrobial and anti-biofilm activities of thymol-loaded chitosan nanogel (Ty-CsNG), free thymol (Ty), and free chitosan nanogel (CsNG) were evaluated against both Gram-negative and Grampositive multidrug-resistant (MDR) bacteria including Staphylococcus aureus, Acinetobacter baumanii, and Pseudomonas aeruginosa strains using the broth microdilution and crystal violet assay, respectively. After treatment of MDR strains with sub-minimum inhibitory concentration (Sub-MIC) of Ty-CsNG, free Ty and CsNG, biofilm gene expression analysis was studied. Moreover, cytotoxicity of Ty-CsNG, free Ty, and CsNG against HEK-293 normal cell line was determined using MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) method. The average size of Ty-CsNG was 82.71 � 9.6 nm, encapsulation efficiency was 76.54 � 0.62 % with stability up to 60 days at 4 °C. Antibacterial activity test revealed that Ty-CsNG reduced the MIC by 4 -6 times in comparison to free thymol. In addition, the expression of biofilm-related genes including ompA, and pgaB were significantly down-regulated after treatment of strains with Ty-CsNG (P < 0.05). In addition, free CsNG displayed negligible cytotoxicity against HEK-293 normal cell lines and presented a biocompatible nanoscale delivery system. Based on the results, it can be concluded that Ty-CsNG can be considered a promising candidate for enhancing antimicrobial and anti-biofilm activities.

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In the present study, the antibacterial and antibiofilm effects of Thymol-based chitosan nanogels were investigated. After clinical screening of MDR strains from the hospital environment, the morphological characteristics of the synthesized nanoparticles were identified using SEM, DLS, XRD and FTIR and the efficiency of encapsulation, stability and drug release were evaluated. The expression of OmpA and PgaB biofilm genes were determined by q-Real-Time PCR and the antibacterial and cytotoxic properties of the nanoparticles were determined by well diffusion and MTT methods, respectively. Nanoparticles with a size of 82.71 nm, encapsulation efficiency of 76.54% and stability up to 60 days at 4 °C were prepared. The results of the biological study showed strong antibacterial properties of Thymol-based chitosan nanoparticles by reducing the expression of OmpA and PgaB biofilm genes at a significant level of P ≤ 0.05 and reducing antibiotic resistance compared to the free drug thymol and chitosan nanogels. Thymol-based chitosan nanogels at concentrations of 0.125 to 256μg/mL showed the lowest cytotoxicity against HEK-293 compared to chitosan and free Thymol nanogels. The results showed very strong antibacterial properties of Thymol-based chitosan nanogels against MDR strains such as Staphylococcus, Acinetobacter and Pseudomonas as the challenging bacteria of the century.

In the present study, the antibacterial and antibiofilm effects of Thymol-based chitosan nanogels were investigated. After clinical screening of MDR strains from the hospital environment, the morphological characteristics of the synthesized nanoparticles were identified using SEM, DLS, XRD and FTIR and the efficiency of encapsulation, stability and drug release were evaluated. The expression of OmpA and PgaB biofilm genes were determined by q-Real-Time PCR and the antibacterial and cytotoxic properties of the nanoparticles were determined by well diffusion and MTT methods, respectively. Nanoparticles with a size of 82.71 nm, encapsulation efficiency of 76.54% and stability up to 60 days at 4 °C were prepared. The results of the biological study showed strong antibacterial properties of Thymol-based chitosan nanoparticles by reducing the expression of OmpA and PgaB biofilm genes at a significant level of P ≤ 0.05 and reducing antibiotic resistance compared to the free drug thymol and chitosan nanogels. Thymol-based chitosan nanogels at concentrations of 0.125 to 256μg/mL showed the lowest cytotoxicity against HEK-293 compared to chitosan and free Thymol nanogels. The results showed very strong antibacterial properties of Thymol-based chitosan nanogels against MDR strains such as Staphylococcus, Acinetobacter and Pseudomonas as the challenging bacteria of the century.