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

## TL;DR

This study examines antibiotic-resistant E. coli in poultry in Bosnia and Herzegovina, finding high levels of resistance linked to ESBL/pAmpC genes.

## Contribution

The study provides a detailed molecular and phenotypic analysis of ESBL/pAmpC resistance in poultry-derived E. coli in Bosnia and Herzegovina.

## Key findings

- ESBL phenotypes were detected in 52.5% of E. coli isolates.
- Multidrug resistance was highly prevalent across all compartments of the poultry production chain.
- blaTEM was the most common ESBL/pAmpC gene, often occurring in multi-gene combinations.

## Abstract

Antimicrobial resistance (AMR) in poultry-associated Escherichia coli (E. coli) 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 E. coli 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 E. coli 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 blaTEM predominating. Gene pattern analysis indicated that blaTEM occurred most frequently as a single determinant and as part of the predominant multi-gene combinations, most notably blaTEM + blaCMY and blaTEM + blaCTX-M, while blaSHV was sporadic. Carbapenemase genes (blaKPC, blaNDM, blaGES, blaOXA-48) and mcr-1 to mcr-9 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.