Unveiling the synergistic enhancement of cefotaxime efficacy with magnetic iron nanoparticles using co-culture technique and tooth model: a promising approach to combat antibiotic resistance.

This study aims to hydrothermally synthesize magnetic iron nanoparticles (MNPs), conjugate them with cefotaxime (CTX), evaluate their efficacy against Escherichia coli strains (AK3 and AK9), and investigate the antibacterial mechanisms involved. The synthesized MNPs exhibited a crystalline structure in X-ray diffraction (XRD), the associated functional groups were confirmed by Fourier transform infrared spectroscopy (FTIR), and the morphology was confirmed through scanning electron microscopy (SEM) and transmission electron microscopy (TEM), with particle sizes ranging from 16.4 nm to 88.2 nm. Conjugation with CTX was confirmed using UV-Vis spectroscopy, FTIR, and dynamic light scattering (DLS), which showed an increased hydrodynamic diameter. The minimum inhibitory concentration (MIC) of CTX was high against the two E. coli strains (46.87 µg/mL and 750 µg/mL), whereas MNPs-conjugated CTX showed strong inhibition at lower doses (11.71 µg/mL and 46.87 µg/mL). Sub-MIC assays demonstrated that MNPs-conjugated CTX significantly inhibited biofilm formation, reduced β-lactamase expression to 22% and 32% in the two strains, respectively, and generated high levels of Reactive Oxygen Species (ROS). Colony-forming unit (CFU) analysis showed enhanced bactericidal activity, with reductions of 1.86 log₁₀ (AK3) and 1.63 log₁₀ (AK9). MNPs-conjugated CTX exhibited minimal cytotoxicity, maintaining 100% viability in HEK293T cells at 23 and 5 µg/mL, and improved cell survival in infected co-cultures to 73.39% (AK3) and 68.97% (AK9). SEM imaging of a tooth biofilm model revealed pronounced biofilm disruption after treatment with MNPs-conjugated CTX. These findings highlight MNPs-conjugated CTX as a promising nanoformulation for treating drug-resistant E. coli infections and support its potential for future biomedical applications.