Gram-negative antimicrobial-resistant bacteria in wild and captive birds: a narrative review of ecological niches and One Health implications

Antimicrobial resistance (AMR) in birds is increasingly investigated because wild and captive birds can encounter resistant bacteria at interfaces involving human activity, other animals, and environmental contamination. This narrative review synthesizes reports of antimicrobial-resistant Gram-negative bacteria in wild, captive, and other non-poultry avian populations. Rather than treating all detections as equivalent, the evidence is interpreted across distinct levels: bacterial occurrence or carriage, phenotypic resistance, antimicrobial resistance genes (ARGs), mobile genetic elements (MGEs), bacterial lineage relatedness, and epidemiological or experimentally demonstrated transmission. The literature shows recurrent detection of ESBL-producing Enterobacterales , bla CTX-M genes, multidrug-resistant phenotypes, and diverse ARGs across multiple ecological settings. However, substantial heterogeneity in sampling, bacterial recovery, antimicrobial susceptibility testing, and molecular characterization limits direct comparison among studies and restricts inference regarding persistence, dissemination, and transmission. The central contribution of this review is therefore an ecological and molecular evidence framework that distinguishes exposure and carriage from persistence, genetic mobility, genomic relatedness, and transmission. The review also identifies methodological priorities, including harmonized sampling and susceptibility testing, longitudinal studies, cross-compartment sampling, genomic characterization, and explicit integration of ecological and epidemiological data.