Polyclonal distribution and predicted plasmid context of ESBL- and AmpC-associated resistance in chicken-derived Escherichia coli from Hungary.

BACKGROUND

Poultry-associated Escherichia coli can harbor clinically relevant antimicrobial resistance determinants, but the clonal and mobile-genetic backgrounds of β-lactam resistance remain incompletely characterized in Central European production systems. We investigated a phenotypically ESBL-suspect collection of 87 E. coli isolates recovered from tracheal and cloacal samples collected on 23 commercial chicken farms in Hungary between 2022 and 2023.

METHODS

Antimicrobial susceptibility testing was integrated with whole-genome sequencing, allele-level resistance-gene identification, Achtman multilocus sequence typing, predicted plasmid reconstruction, pan-genome analysis and recombination-filtered core-genome phylogenetics.

RESULTS

Phenotypic ESBL production was confirmed in 19/87 isolates (21.8%). The principal ESBL alleles were bla CTX-M-1 (11/87) and bla CTX-M-15 (3/87), while bla CMY-2 was detected in four isolates. Complete Achtman sequence types were assigned to 44 isolates, representing 30 sequence types. Ten of 11 bla CTX-M-1 occurrences were computationally assigned by MOB-suite to predicted conjugative IncI-gamma/K1 plasmid bins. The recombination-filtered phylogeny resolved multiple distinct lineages, showing that ESBL positivity and CTX-M carriage were not restricted to a single clone.

CONCLUSION

These findings indicate that ESBL- and AmpC-associated resistance occurred across diverse chicken-derived E. coli backgrounds and was frequently associated with predicted plasmid contexts.