# In Vitro and In Vivo Evaluation of Nitroxoline as an Effective Antimicrobial Alternative to Poultry Production

## TL;DR

Nitroxoline is a promising alternative to antibiotics in poultry, reducing bacterial loads and improving growth without resistance risks.

## Contribution

Nitroxoline is identified as a new antimicrobial candidate for poultry with low resistance potential and effective in vivo performance.

## Key findings

- NTX shows potent in vitro antibacterial activity and low resistance.
- NTX reduces liver bacterial loads in Salmonella-infected chickens and improves weight gain.
- NTX modulates caecal microbiota, increasing beneficial bacteria like Faecalibacterium and Lactobacillus.

## Abstract

Background: Antimicrobial resistance is a major global challenge that is exacerbated by extensive antibiotic use in livestock farming. Identifying effective alternatives to widely used human antibiotics in animal production is vital to safeguard vital human medicines and ensure sustainable food systems. Here we describe studies identifying nitroxoline (NTX) as a promising antimicrobial candidate for use in poultry production. Methods: The antibacterial activity and resistance potential of NTX were assessed in vitro. In vivo studies in chickens evaluated tolerance, therapeutic efficacy in Salmonella-infected birds, pharmacokinetics, tissue residue depletion, growth performance, and effects on caecal microbiota. NTX was administered in-feed at different dose levels. Pharmacokinetic parameters and withdrawal periods were determined, and caecal microbiota composition was analysed using ribosomal RNA 16S sequencing. Results: NTX exhibits potent broad-spectrum antibacterial activity in vitro and low levels of resistance. NTX is well-tolerated in chickens at 500 mg/kg in-feed for 7 days and substantially reduces liver bacterial loads at 100 mg/kg in Salmonella-infected chickens. Pharmacokinetic and residue analyses reveal NTX manifests rapid absorption and distribution, high oral bioavailability (86%), and efficient tissue clearance with a 17-day withdrawal period required for skin-plus-fat clearance. NTX supplementation is associated with increased weight gain and improved feed efficiency compared to the control group, with performance comparable to chlortetracycline. Microbiota analysis indicates modulation of caecal bacterial communities, including increased Faecalibacterium and Lactobacillus. Conclusions: These results indicate that NTX is a viable alternative to important human antibiotics widely deployed in poultry production, offering a potential approach to minimise antimicrobial resistance whilst maintaining animal health and food biosafety.