Phenotypic and Molecular Characterization of ESBL/pAmpC-Associated Resistance in Poultry- and Hatchery-Derived Escherichia coli in Bosnia and Herzegovina

Antimicrobial resistance (AMR) in poultry-associated <i>Escherichia coli</i> (<i>E. coli</i>) is a persistent One Health concern, particularly when ESBL/pAmpC determinants co-occur with resistance to multiple antimicrobial classes. Between March and October 2024, we investigated commensal <i>E. coli</i> from three interconnected compartments of the poultry production chain in Bosnia and Herzegovina (parent-breeder flocks, commercial broiler farms, hatchery-associated material). A total of 333 samples were examined, and 99 <i>E. coli</i> isolates were recovered (29.7%). Phenotypic characterization included ESBL confirmation, disk diffusion susceptibility testing, and EUVSEC broth microdilution. Targeted real-time PCR assays were used to screen key ESBL/pAmpC-associated genes and selected carbapenemase and plasmid-mediated colistin resistance targets within the targeted panel. ESBL phenotypes were detected in 52/99 isolates (52.5%), and multidrug resistance was highly prevalent across compartments (93/99; 93.9%). ESBL/pAmpC-associated genes were detected in 91/99 isolates (91.9%), with <i>bla_TEM</i> predominating. Gene pattern analysis indicated that <i>bla_TEM</i> occurred most frequently as a single determinant and as part of the predominant multi-gene combinations, most notably <i>bla_TEM</i> + <i>bla_CMY</i> and <i>bla_TEM</i> + <i>bla_CTX-M</i>, while <i>bla_SHV</i> was sporadic. Carbapenemase genes (<i>bla_KPC</i>, <i>bla_NDM</i>, <i>bla_GES</i>, <i>bla_OXA-</i>₄₈) and <i>mcr-1</i> to <i>mcr-9</i> were not detected. Overall, our findings indicate a substantial ESBL/MDR burden throughout the poultry production chain, supporting the need for strengthening antimicrobial stewardship and biosecurity measures across both farms and hatcheries.