# Persistence and Dissemination of Enrofloxacin and Ciprofloxacin Residues: The Hidden Role of Litter and Droppings in the Emergence of Antimicrobial Resistance

## TL;DR

This study shows that enrofloxacin and ciprofloxacin residues in poultry litter and droppings can persist for weeks and contribute to the development of antibiotic-resistant E. coli.

## Contribution

The study identifies poultry litter and droppings as reservoirs and vectors for antimicrobial residues and resistance dissemination.

## Key findings

- Enrofloxacin and ciprofloxacin residues persisted in litter and droppings for up to 18 days post-treatment.
- Residue presence correlated with increased E. coli resistance rates in treated and nearby untreated groups.
- Environmental dissemination of residues was confirmed, highlighting the need for improved waste management.

## Abstract

Enrofloxacin is a widely used antimicrobial agent for treating poultry diseases. However, the presence of its residues is a significant concern due to their introduction into the production environment and the selection of quinolone-resistant pathogens, with litter and droppings from birds being a potential source of contamination as there are no regulations establishing maximum residue limits in these matrices. This study aimed to evaluate litter and droppings as reservoirs of enrofloxacin and ciprofloxacin residues and their relationship to the development of antimicrobial resistance in Escherichia coli in a controlled poultry production model. Following enrofloxacin treatment (10 mg·kg−1 every 24 h for 5 days), high concentrations of residues were detected in the litter and droppings of treated birds exceeding the minimal inhibitory concentration of E. coli to enrofloxacin, reaching elevated levels in feces by day 3 post-treatment and remaining above the limit of quantification until day 18. Ciprofloxacin residues persisted in feces until day 12 and were still detectable in litter on day 18. The presence of residues in untreated groups suggests environmental dissemination. Regression analysis showed a significant positive relationship between residue concentration and resistance rate. These findings highlight the potential of poultry litter and droppings as reservoirs and vectors of antimicrobial residues and resistance, demonstrating the persistence and dissemination of residues in the production environment, as well as their impact on E. coli resistance. This underscores the importance of proper waste management and mitigating its negative impact from a One Health perspective.

The objective of this study was to evaluate the persistence and environmental dissemination of enrofloxacin (EFX) and its metabolite ciprofloxacin (CFX) residues in poultry systems, as well as their effect on antimicrobial resistance in Escherichia coli. The experimental design included three groups: one treated group (A) and two untreated groups (B.1 and B.2), located in pens adjacent to or within 30 cm of group A to assess residue transfer. Birds in group A received EFX orally (10 mg·kg−1 every 24 h for 5 days) via orogastric tube. EFX and CFX residues persisted in litter and excreta for up to 18 days post-treatment, reaching initial concentrations of 20,968 µg·kg−1 in litter and 884.8 µg·kg−1 in droppings in group A. Significant differences were detected between groups (Kruskal–Wallis, p < 0.05), confirming greater accumulation in the treated group and environmental dissemination. E. coli isolates obtained from litter and droppings from group A showed 73% resistance after treatment and correlated positively with residue concentration (ρ = 0.53). While the untreated groups B.1 and B.2 showed resistance rates of 24% and 13%, respectively, the control group exhibited a resistance rate of 3.3%. This study shows the detection of low levels of EXF and CFX residues in the litter of untreated groups, indicating limited dispersion. These findings highlight the importance of proper byproduct management and targeted environmental monitoring within the One Health framework, as continuous environmental exposure over time, combined with the persistence of this compound, may contribute to the selection of resistant bacteria.