Design, Development, and Experimental Validation of Chitosan-based Nanocarriers Encapsulating Novel Thiazole–Flavonoid Hybrids for Targeted Therapy of Carbapenem-Resistant Enterobacterales: Formulation Optimization, Spectroscopic and Chromatographic Chara

Abstract

The increasing prevalence of carbapenem-resistant Enterobacterales (CRE) has created an urgent need for novel antibacterial agents and effective drug-delivery systems. The present study was designed to develop and experimentally evaluate chitosan-based nanocarriers encapsulating novel thiazole–flavonoid hybrids for enhanced antibacterial and anti-biofilm activity against CRE. Thiazole–flavonoid hybrids were synthesized and characterized using Fourier-transform infrared spectroscopy (FTIR), ^1H/^13C-nuclear magnetic resonance (NMR), mass spectrometry, UV–Visible spectroscopy, and high-performance liquid chromatography (HPLC). The lead hybrid, TFH-3, was incorporated into chitosan nanoparticles using an ionic-gelation approach and optimized with respect to particle size, polydispersity index (PDI), zeta potential, entrapment efficiency, and drug-loading capacity. The optimized formulation (CTF-3) exhibited a particle size of approximately 168 nm, PDI of 0.214, positive zeta potential of approximately +31.6 mV, and entrapment efficiency of 87.8%. In-vitro release studies demonstrated sustained release of TFH-3 from CTF-3 compared with the free compound, with the Korsmeyer–Peppas model providing the best fit to the release data. CTF-3 demonstrated enhanced antibacterial activity against the tested CRE isolates, with lower minimum inhibitory and bactericidal concentrations than free TFH-3. Increased membrane permeability and cellular leakage suggested bacterial membrane disruption as a possible contributing mechanism. The nanoformulation also showed improved inhibition of biofilm formation and activity against established biofilms. Cytotoxicity evaluation indicated comparatively higher mammalian-cell viability and a higher apparent CC₅₀ for CTF-3 than free TFH-3. Overall, the findings support chitosan nanoencapsulation as a promising strategy for improving the delivery and antibacterial performance of thiazole–flavonoid hybrids against drug-resistant bacterial pathogens. Further pharmacokinetic, in-vivo efficacy, toxicity, and formulation-scale-up studies are required to establish their translational potential.