Enhanced therapeutic efficacy of biogenic nanosilver-conjugated thymol: In vitro and in vivo evaluation against emerging multi-drug resistant microbes

Abstract

Phytochemicals and nanoparticles (NPs) despite having strong antibacterial activity, their limited stability and safety prevent their widespread biomedical and environmental applications. Therefore, the bio-efficacy and environmental safety of both can be increased by fabricating and conjugating them using eco-friendly processes. Herein, the impact of a novel green nanomedicine, nanosilver-conjugated thymol (AgT), was evaluated against multi-drug resistant enteroaggregative Escherichia coli (MDR-EAEC) strains using in vitro and in vivo (Galleria mellonella) assays. Characterization of AgT by UV-Vis and FTIR spectroscopy demonstrated the conjugation of thymol with biogenic nanosilver with a loading capacity of 16.60 � 0.24%. Electron microscopy revealed mono-dispersed spherical morphology with a size of 15.077 � 3.34 nm. The minimum inhibitory concentration (4-16 ?g/mL) and minimum bactericidal concentration (8-16 ?g/mL) were five to six-fold times lower than thymol. The antibacterial efficacy of AgT was at par with meropenem in the in vitro time-kill assay. Moreover, AgT was tested safe against gut lactobacilli, sheep erythrocytes, RAW 264.7 and HEp-2 cell lines; stable at various high-end temperatures, pH, proteases, cationic salts, and host sera. G. mellonella larvae treated with AgT exhibited higher survival rates and safety with reduced MDR-EAEC counts. Overall, compared to thymol, AgT showed promising therapeutic potential with improved safety.