**Background:** Third-generation cephalosporin-resistant (3GCR) and extended-spectrum β-lactamase (ESBL)-producing Escherichia coli pose a significant threat to human and animal health worldwide. In low- and middle-income countries, small-scale food animal production is common, and antimicrobials are often available over the counter with limited veterinary oversight. This study aimed to estimate the prevalence of ceftriaxone-resistant (CR) and ESBL-producing E. coli among domestic animals in semirural parishes east of Quito, Ecuador, and to identify household-level risk factors for carriage.
**Methods:** This analysis was part of a larger repeated measures study conducted across 7 semirural parishes east of Quito, Ecuador. Data were collected over three 20-week cycles from July 2018 to May 2019. Households were eligible if they had a primary caregiver ≥18 years, a child aged 6 months to 5 years, and provided informed consent. A total of 304 households with at least one animal fecal sample were included. Trained personnel administered a validated antibiotic knowledge, attitudes, and practices (KAP) survey covering animal care, sanitation, feeding practices, proximity to commercial food animal facilities, antimicrobial use, and socioeconomic factors. Fresh environmental animal fecal samples (n=1195) were collected aseptically and processed within 5 hours. E. coli was isolated on MacConkey agar with ceftriaxone (2 mg/L). Antimicrobial susceptibility was assessed via Kirby-Bauer disk diffusion for 12 antimicrobials. ESBL production was defined by double disk synergy. Primary outcomes were CR and ESBL-producing E. coli carriage in dogs and food animals. Multivariable logistic regression with generalized estimating equations (GEE) and exchangeable working correlation was used to estimate adjusted odds ratios (OR) with robust 95% confidence intervals (CI).
**Key Results:** Overall, CR E. coli was detected in 56% (670/1195) and ESBL-producing E. coli in 10% (123/1195) of all fecal samples. Prevalence varied by species: CR was highest in ducks (82%), pigs (72%), chickens (70%), and dogs (68%); ESBL was highest in pigs (16%), dogs (13%), chickens (12%), and ducks (9%). At the household level, 87% (264/304) had at least one CR-positive sample and 32% (96/304) had at least one ESBL-positive sample. For dogs, increased odds of CR E. coli carriage were associated with living within 5 km of >5 commercial food animal facilities (OR 1.72, 95% CI 1.15–2.58) and detecting poultry odors (OR 1.84, 95% CI 1.21–2.79). Use of antibiotics based on veterinary/pharmacy recommendation was protective (OR 0.18, 95% CI 0.04–0.96). For canine ESBL-producing E. coli, increased odds were associated with recent antimicrobial use in any household animal (OR 2.69, 95% CI 1.02–7.10) and purchasing antibiotics from pet food stores (OR 6.83, 95% CI 1.32–35.35). Use of commercial feed was protective for both CR (OR 0.65, 95% CI 0.43–0.97) and ESBL (OR 0.50, 95% CI 0.26–0.96) in dogs. For food animals, decreased odds of CR E. coli were associated with owning >3 species (OR 0.64, 95% CI 0.42–0.97), using antibiotics for growth promotion (OR 0.41, 95% CI 0.19–0.89), and purchasing antibiotics from pet food stores (OR 0.47, 95% CI 0.25–0.89). Increased odds of ESBL-producing E. coli in food animals were associated with households of >5 people (OR 2.22, 95% CI 1.23–3.99) and location within 1 km of a commercial food animal facility (OR 2.57, 95% CI 1.08–6.12).
**Clinical Implications:** This study demonstrates a high burden of CR and ESBL-producing E. coli among domestic animals in semirural Ecuador, particularly in dogs, pigs, chickens, and ducks. The association between proximity to commercial food animal facilities and increased odds of resistance in both dogs and food animals suggests potential spillover from intensive production systems. The finding that antimicrobial use in any household animal increased canine ESBL carriage, while veterinary-recommended antibiotic use was protective, highlights the importance of antimicrobial stewardship and veterinary oversight. The protective effect of commercial feed use in dogs may relate to reduced raw meat consumption. These results underscore the complexity of antimicrobial resistance in small-scale production settings and the need for context-specific, One Health interventions that address human, animal, and environmental health simultaneously.