Avian colibacillosis is one of the most devastating diseases in chickens, resulting in high economic losses as well as high morbidity and mortality. Colistin is considered one of the most effective antimicrobials against colibacillosis. The recent discovery of mobile colistin resistance (mcr-1) determinants in humans and animals raised serious concerns about its potential dissemination among bacteria. This study aimed to investigate the presence of mcr1 gene among E. coli isolates in broiler chickens infected with colibacillosis. As an experimental design was performed on broiler chickens after molecular detection of mcr-1 gene to explore the efficacy of neomycin as a hydrophobic antibiotic wither in the mcr-1 absence or its existence after oral inoculation of E. coli strains. . Results revealed the high prevalence of colibacillosis among broiler farms in addition to highly spread of colistin resistance among E. coli isolates either through isolation on specific colistin resistance medium or molecular detection of the mcr-1 gene. On other hand, by histological examination we observed that the presence of the mcr-1 gene among E. coli isolates improved the treatment efficacy of the hydrophobic antibiotic. As a result of the significant antibiotic resistance issues and high risk of transmission of antibiotic-resistant bacteria and genes to humans, the development of antibacterials only for animal uses without cross-resistance to existing antibiotics might afford a solution in the future. Although there is an increase in acquired antibiotic resistance genes, it is possible to take advantage of this phenomenon, which in turn led to an increase in the sensitivity of some other antibiotics. Therefore, we recommend studying pharmacokinetic of antibacterials and making the most of this widespread phenomenon.

Escherichia coli (E.coli) infections pose significant health risks to poultry and humans globally. In the face of antibiotic-resistant strains, metal oxide nanoparticles and plant extracts have emerged as promising alternatives. This study evaluated the effectiveness of copper oxide nanoparticles (CuO-NPs) and black elderberry extract (BEE) against E. coli O78 infection in specific pathogen-free chicks. The birds were divided into four groups: a negative control NC, a positive control (PC; challenged with E. coli O78), CuO-NPs treatment post-challenge, and BEE treatment post-challenge. Various parameters, including clinical signs, organ lesions, bacterial load, biochemical markers, and histopathology, were assessed. Both CuO-NPs and BEE demonstrated a reduction in clinical morbidity, organ damage, and E. coli counts compared to the PC. However, BEE exhibited slightly greater efficacy in alleviating liver and kidney dysfunction. Overall, CuO-NPs and BEE hold therapeutic potential against avian colibacillosis, likely acting through antimicrobial and immunomodulatory mechanisms. These findings underscore the potential of bio-based nanoparticles and plant extracts as safer, multi-modal alternatives to antibiotics for avian colibacillosis. Further optimization and mechanistic studies are needed to support their clinical application.