Enhanced antibacterial activity of nano-conjugates of cephradine against multidrug-resistant bacteria: Experimental and theoretical insights

Background: Currently, bacteria are getting resistant to antibiotics which pose a serious threat to human health. In this scenario, new nanoantibiotics have the potential to avoid the emerging bacterial resistance mechanisms. Hence, this study attempts to unveil the activity enhancement of Cephradine (Cfdn) by using experimental and theoretical investigations.Methods: Silver (Ag) and gold (Au) nanoparticles (NPs) stabilized with Cfdn (Cfdn-AgNPs and Cfdn-AuNPs) were synthesized using a one-pot reduction method, and their characteristics were analyzed using atomic force microscope (AFM), scanning electron microscope (SEM), Fouriertransform infrared (FT-IR) spectroscopy, UV-visible spectroscopy. The stability of the NPs was evaluated under different physiological conditions. The antimicrobial action of Cfdn, when conjugated with the Ag and Au NPs, was demonstrated by conducting experiments with multidrugresistant Staphylococcus aureus (S. aureus) cell cultures. AFM images were used to observe changes in S. aureus cell morphology before and after treatment with free and conjugated Cfdn.Moreover, theoretical analysis was carried out to further validate the enhanced activities of Cfdn-AgNPs and Cfdn-AuNPs.The spherical (20-55 nm) Cfdn-AgNPs and Cfdn-AuNPs demonstrated good stability under saline, pH, and thermal conditions. Interestingly, a significant improvement was achieved in the antibacterial activity, with Cfdn-AgNPs and Cfdn-AuNPs exhibiting activity enhancements of up to 2 and 6 times, respectively. AFM images confirmed improved kinetics of the antibiotic upon conjugation, where Cfdn alone did not cause sufficient damage to bacterial membranes even after a 4-hour treatment, whereas treatment with Cfdn-AgNPs and Cfdn-AuNPs resulted in effective cell membrane damage and complete disruption of cell morphology within the same timeframe. Moreover, theoretical simulation employing density functional theory (DFT) validated the enhanced antibacterial potential of Cfdn-AgNPs and Cfdn-AuNPs. Interestingly, cytotoxicity analysis revealed improved cytocompatibility of the NPs after conjugation with Cfdn.We established a systematic strategy for the development of innovative nanoantibiotics based on experimental and theoretical evidence, which can be exploited in the battle against bacterial resistance.