Abstract
Multidrug-resistant (MDR) Escherichia coli are a zoonotic pathogen with limited therapeutic options that are a serious threat in veterinary settings worldwide. The present study aimed to assess the antimicrobial activity of gold nanoparticles (AuNPs) against MDR E. coli of veterinary origin. 100 samples (faecal, milk, nasal and environmental swabs) were collected and processed for bacterial isolation and identification by the application of standard microbiological, biochemical and analytical techniques. Antibiotic susceptibility testing was conducted using the Kirby–Bauer method, and MDR isolates were chosen for further analysis. The gold nanoparticles were prepared by a chemical reduction process, and the prepared gold nanoparticles were characterized by UV-visible spectroscopy and transmission electron microscopy (TEM). The zone of inhibition, minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were calculated by using antibacterial activity using the agar well diffusion method and broth micro dilution method. Of the 68 confirmed E. coli isolates, 52 (76.4%) were MDR. AuNPs showed good antibacterial activity with increasing concentration. The MIC and MBC values indicated strong bactericidal activity at lower concentrations. The morphological analysis showed the presence of structural damage to the bacterial cell wall, with the disruption of the membrane and the leakage of the cytoplasmic content, thus indicating a multi-targeted action against the bacteria. The results showed that AuNPs have a great potential to be used as alternative antimicrobial agents in veterinary medicine against MDR E. coli. The resistance mechanisms that they have to overcome, such as efflux pumps and biofilm formation, provide the promise that they could help solve the global problem of antimicrobial resistance