# Antimicrobial Use and Epidemiological Resistance Profiles of Commensal Escherichia coli from Swine Farms in Córdoba, Argentina

## TL;DR

This study examines antimicrobial use and resistance in E. coli from swine farms in Córdoba, Argentina, revealing high levels of multidrug resistance and the need for better antimicrobial stewardship.

## Contribution

The study provides a detailed characterization of antimicrobial use and resistance profiles in commensal E. coli from swine farms using epidemiological cut-off values.

## Key findings

- Antimicrobial use was frequent and primarily prophylactic, with macrolides and amoxicillin being the most commonly used.
- High proportions of non-wild-type E. coli were observed for several antimicrobials, with 92% of isolates classified as multidrug resistant.
- Extended-spectrum β-lactamase-producing phenotypes were detected, indicating a stable intestinal resistome in swine.

## Abstract

Background/Objectives: The expansion of intensive swine production in Córdoba, Argentina, underscores the need to assess the risks associated with antimicrobial (AM) use, whose extensive application has driven antimicrobial resistance, a major global threat within the One Health framework. This study aimed to characterize AM use practices and evaluate the epidemiological resistance profiles (non-wild-type phenotypes, NWT) of commensal Escherichia coli of fecal origin from swine farms, using epidemiological cut-off values (ECOFFs) as a surveillance criterion. Methods: An observational cross-sectional study was conducted in 19 farrow-to-finish farms in Córdoba during 2023. Information on AM use (prophylaxis, metaphylaxis, treatment) across production categories was collected. A total of 437 E. coli isolates were obtained from fecal samples, and minimum inhibitory concentrations (MICs) were determined for 10 AMs of critical importance for human and animal health. NWT phenotypes were classified according to EUCAST ECOFFs, and multidrug resistance (MDR) was assessed. Results: AM use was frequent and predominantly prophylactic (89.5% of farms), mainly through mass medication (66.3%), with macrolides and amoxicillin being the most commonly administered AMs. NWT proportions were extremely high (90–92%) for ampicillin, tetracyclines, and chloramphenicol and substantial for ciprofloxacin (50.6%), sulfamethoxazole (68.2%), and trimethoprim (44.9%). Extended-spectrum β-lactamase (ESBL)-producing phenotypes were detected. Alarmingly, 92% of isolates were classified as MDR E. coli, with homogeneous distribution across production categories. Conclusions: Findings reveal intensive and largely empirical AM use that has consolidated a stable intestinal resistome in the swine population. High MDR levels, even in categories with limited direct AM exposure or involving banned compounds, suggest that co-selection and horizontal gene transfer are key drivers of resistance. This scenario highlights the urgent need to strengthen integrated surveillance and promote prudent AM use strategies under the One Health approach to preserve therapeutic efficacy.