Preparation, characterization, and evaluation of chitosan-thymol nanoparticles for antibacterial and antibiofilm activities against catheter-associated uropathogenic Escherichia coli.

Uropathogenic Escherichia coli (UPEC) is a major cause of urinary tract infections (UTIs) and is capable of forming biofilms on inert surfaces, contributing to persistent and recurrent infections. Given the limitations of conventional antibiotics, alternative strategies are needed to control multidrug-resistant (MDR) UPEC. This study aimed to evaluate the antibacterial and antibiofilm effects of thymol-loaded chitosan nanoparticles (TLCNPs) against MDR UPEC isolates urinary catheters. TLCNPs were prepared using the ionotropic gelation method and characterized by scanning electron microscopy (SEM), dynamic light scattering (DLS), and Fourier-transform infrared spectroscopy (FTIR). The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were determined using the broth microdilution method. Antibiofilm activity was assessed by the microtiter plate crystal violet assay. The relative expression of fimA and fimH genes was evaluated using real-time PCR. Cytotoxicity was assessed by the MTT assay on a human bladder carcinoma cell line (EJ138). The results showed that TLCNPs exhibited antibacterial activity against MDR UPEC isolates, with MIC and MBC values of 625 µg/mL. Biofilm formation was reduced by up to 76.2 ± 0.6% at ½ MIC concentration. Although a decrease in the relative expression of fimA and fimH genes was observed following treatment with TLCNPs, these changes were not statistically significant. Cytotoxicity assays indicated that more than 70% of EJ138 cells remained viable after 24 h, and over 50% after 48 h at ½ MIC. Overall, this study evaluated the antibacterial, antibiofilm, and preliminary safety profile of thymol-loaded chitosan nanoparticles against MDR UPEC, providing experimental data for their further investigation as a potential adjunct approach for biofilm-associated UTIs.