Abstract
Background:
Respiratory infections in poultry, particularly those caused by Escherichia coli, are a major concern in veterinary medicine due to their economic impact and increasing antibiotic resistance. Nanotechnology-based antimicrobial delivery systems have emerged as promising alternatives to conventional treatments.

Aim:
This study aimed to evaluate the cytotoxicity and antibacterial activity of various nano-antibiotic formulations—comprising antibiotics, herbal extracts, and silver nanoparticles—against E. coli strains isolated from chickens with respiratory disease.

Method:
The nanoantibiotic formulations were developed by the Department of Biomedical Nanomaterials, Institute of Materials Science, Vietnam, and included combinations such as polymer–garlic, polymer–Phyllanthus urinaria, polymer–garlic–silver, polymer–Phyllanthus urinaria–silver, polymer–doxycycline + florfenicol, polymer–doxycycline + oxytetracycline, and their respective silver-conjugated forms, along with chitosan. Cytotoxicity was assessed using Vero cells, and antibacterial activity was determined in vitro using the dilution method in 96-well flat-bottom plates.

Results:
The study found that cytotoxic effects were observed at dilutions of 1:32 and 1:64 when the formulations combined antibiotics, herbal extracts, and nanosilver. Importantly, this combination significantly enhanced bactericidal activity compared with formulations containing only antibiotics or herbal extracts.

Conclusion:
The integration of nanosilver with antibiotics and herbal extracts in nanoparticle systems shows promising antibacterial efficacy against E. coli, with tolerable cytotoxicity at appropriate dilutions. These findings suggest the potential of such nanoformulations as effective alternatives in managing bacterial respiratory infections in poultry.

Key words: In vitro nanoparticle antibiotic, Complex respiratory bacteria, E. coli, Chicken