Sessions

Antimicrobial resistance is a major animal-health and One Health challenge in pig production. This study characterized the antimicrobial susceptibility of Escherichia coli isolates from large-scale pig farms in Western Transdanubia, Hungary, and evaluated age- and farm-related differences, phenotypically suspected extended-spectrum beta-lactamase (ESBL) production and multidrug resistance (MDR).

A total of 140 E. coli isolates recovered from rectal swabs collected on three farms were examined. Samples originated from neonatal, four-week-old and six-week-old pigs. Minimum inhibitory concentrations (MICs) were determined by standard broth microdilution, and resistance was interpreted using prespecified interpretive thresholds. MIC₅₀ and MIC₉₀ values, suspected ESBL status, MDR, extensively drug-resistant (XDR) and pandrug-resistant (PDR) categories, and pairwise co-resistance associations were determined. Resistance-profile structure was assessed using Jaccard-distance-based principal coordinates analysis (PCoA) and hierarchical clustering.

The highest resistance rate was observed for amoxicillin (77.1%). Resistance to cefotaxime, cefquinome, doxycycline and ceftiofur was 48.6%, 38.6%, 35.0% and 32.9%, respectively. No imipenem-resistant isolate was detected, while resistance to enrofloxacin, marbofloxacin and colistin was 5.0%, 4.3% and 6.4%. Overall, 37.9% of isolates exhibited an ESBL-suspect phenotype, while 42.1% met the criteria for multidrug resistance; no panel-based XDR or PDR phenotype was identified.

Significant age-group differences were detected for gentamicin and neomycin resistance, both being highest among neonatal pigs and absent among six-week-old animals. Farm-level differences were substantially greater. At Ormándlak, resistance to cefotaxime reached 90.0%, resistance to ceftiofur and cefquinome reached 64.3%, and 74.3% of isolates displayed a suspected ESBL phenotype. Multivariate analysis indicated marked farm-level structuring (PERMANOVA R² = 0.200), although within-group dispersion also differed significantly among farms. Sixty-three distinct patterns were identified, and the strongest co-resistance association occurred between ceftiofur and cefquinome.

The findings demonstrate marked farm-specific heterogeneity and substantial resistance to beta-lactams and extended-spectrum cephalosporins. They support regular farm-level MIC surveillance, targeted molecular confirmation and antimicrobial stewardship integrating phenotypic resistance data with antimicrobial-use records.