Multidrug-resistance in backyard poultry and their link to management and biosecurity conditions in Eastern Spain.

Alternative poultry production systems are increasing due to consumer concerns regarding conventional farming practices and the growing demand for more sustainable systems that promote animal welfare. In this context, backyard poultry keeping for hobby or self-consumption purposes has become increasingly common in both rural and urban areas. However, unlike commercial poultry production, these flocks are often managed with limited biosecurity and sanitary measures, and their role in the maintenance and dissemination of antimicrobial-resistant bacteria remains poorly understood. Therefore, this study aimed to characterize the epidemiological situation of antimicrobial resistance (AMR) in backyard poultry farms in eastern Spain using Escherichia coli as an environmental sentinel bacterium. Owners of backyard poultry across eastern Spain were invited to voluntary take. Epidemiological data on flock management and biosecurity practices were collected to evaluate farm biosecurity levels. For E. coli isolation, cloacal swabs were obtained from up to six hens per farm, and two environmental surface wipes were collected from each facility. In total, 33 backyard poultry farms from 24 localities were randomly sampled. The survey revealed a wide range of biosecurity levels, with low (36.4%) and moderate (57.6%) biosecurity levels being the most common. Overall, 246 samples were collected, yielding 216 E. coli isolates, including 168 from animal samples and 48 from environmental samples. Among animal isolates, 95.8% showed resistance to at least one antimicrobial and 73.8% exhibited a multidrug-resistant (MDR) phenotype. Similarly, 97.9% of environmental isolates were resistant and 75% were MDR. The highest resistance rates in animal and environmental isolates were observed for tetracycline (86.9% and 91.7%, respectively) and ampicillin (82.7% and 85.4%, respectively). These findings reveal a high burden of AMR in backyard poultry environments. The limited implementation of biosecurity measures and frequent contact with wildlife and other animals may contribute to this situation. These results emphasize the importance of including backyard poultry systems in AMR surveillance and control programs under a One Health approach.