Phenotypic antimicrobial resistance patterns of Escherichia coli isolates from healthy chicken and turkey flocks in Hungary differ across poultry production systems.

Antimicrobial resistance (AMR) in Escherichia coli from clinically healthy poultry flocks can indicate antimicrobial selection pressure and the potential entry of resistant bacteria into the food chain. Because chicken and turkey production systems differ, aggregation into a single poultry category may obscure relevant AMR heterogeneity. We characterized phenotypic AMR in 880 E. coli isolates collected in Hungary during 2022-2023 from breeder chickens (n = 98), broiler chickens (n = 185), egg layers (n = 127), broiler turkeys (n = 338), and turkey breeders (n = 132). Susceptibility to 11 antimicrobials representing seven class/group endpoints was determined by broth microdilution using CLSI, EUCAST, and literature-derived interpretive thresholds. Resistance profiles were summarized descriptively and by a fixed seven-cluster exploratory k-means analysis. Associations with production type and sample source were evaluated using county-random-intercept mixed-effects logistic models, with county-fixed-effect Firth logistic models used as sensitivity analyses; resistance-count burden was assessed using Conway-Maxwell-Poisson mixed-effects regression. Multidrug resistance was most frequent in broiler chickens (99.5%), followed by turkey breeders (87.1%) and broiler turkeys (84.3%), and resistance patterns differed across production categories. In resistance-count models, broiler chicken and broiler turkey isolates had higher expected numbers of resistant class/group endpoints than breeder chicken isolates (IRR = 1.63, 95% CI: 1.38-1.93; and IRR = 1.33, 95% CI: 1.20-1.47, respectively). Sensitivity analyses showed that several associations were robust in direction, whereas aminoglycoside/aminocyclitol and folate-pathway estimates were particularly model-dependent because of sparse data and limited geographic overlap. These findings support AMR surveillance stratified by poultry species and production category, while production-type associations should be interpreted within the geographic structure of the present sampling framework.