Influence of housing system on antimicrobial resistance and population structure of extended-spectrum beta-lactamase-producing Escherichia coli in South Korean layer farms

초록

Extended-spectrum (3-lactamase (ESBL)-producing Escherichia coli are widespread in poultry production, posing serious public health risks. However, evidence from commercial layer farms-particularly environmental reservoirs-and direct comparisons between cage and floor housing systems remain limited. In this study, we aimed to investigate the prevalence, antimicrobial resistance (AMR) profiles, (3-lactamase genotypes, and clonal diversity of ESBL-producing E. coli in floor- and cage-housed layer farms in South Korea to inform AMR risk assessment and control strategies. Eighty ESBL-producing E. coli isolates were recovered from 34 environmental samples collected across six farms (three floor-housed and three cage-housed layer farms). All isolates exhibited high resistance to ampicillin and third-generation cephalosporins, whereas susceptibility to imipenem and amikacin was retained. Resistance to tetracycline (45.2% vs. 15.8%; P = 0.005), chloramphenicol (64.3% vs. 31.6%; P = 0.005), and trimethoprim-sulfamethoxazole (54.8% vs. 18.4%; P = 0.001) was higher among floorhoused than cage-housed isolates, resulting in a higher prevalence of multidrug resistance in floor-housed isolates. Genotypic analysis identified blaCTX-M-14 (27.5%) and blaCTX-M-55 (21.3%) as the most prevalent ESBL genes. Among non-ESBL (3-lactamase genes, blaTEM-30 and blaTEM-116 were more frequent in floor-housed isolates, whereas blaTEM-163 predominated in cage-housed isolates. Multilocus sequence typing showed reduced clonal diversity in floor-housed isolates, dominated by ST1718 and ST10, whereas cage-housed isolates displayed broader, more heterogeneous lineages. These findings indicate the association of layer housing systems with differences in AMR burden, (3-lactamase allele distribution, and clonal structure of ESBL-producing E. coli, supporting housing-tailored biosecurity and farm-level surveillance to mitigate dissemination in layer production.

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