Sessions

Antimicrobial resistance is one of the most important veterinary and public health challenges in the treatment of infectious diseases. Accordingly, the investigation of clinically derived bacterial infections occurring in the waterfowl sector is of particular importance, especially in the case of Escherichia coli and Salmonella. The aim of the present study was to assess the antimicrobial resistance situation of bacterial isolates recovered from clinical cases in the Hungarian waterfowl sector, with particular emphasis on these two dominant bacterial species.

The study included isolates obtained from clinical cases in Hungarian waterfowl flocks between 2025 and 2026. Species identification was performed by MALDI–TOF, while phenotypic antimicrobial susceptibility testing was carried out by broth microdilution with determination of minimum inhibitory concentrations (MICs). The results were interpreted according to the recommendations of the Clinical and Laboratory Standards Institute (CLSI) and the European Committee on Antimicrobial Susceptibility Testing (EUCAST), and MIC₅₀, MIC₉₀, as well as the occurrence of multidrug-resistant (MDR) phenotypes, were also determined.

A total of 38 isolates were included in the analysis, of which 28 were E. coli and 10 were Salmonella. In the E. coli population, the most unfavorable susceptibility profile was observed for amoxicillin, potentiated sulfonamide, and enrofloxacin, while substantial resistance was also detected to florfenicol and spectinomycin. The most favorable activity was shown by ceftriaxone, colistin, and imipenem. The MDR phenotype was present in 53.6% of the E. coli isolates. In contrast, the Salmonella isolates showed an overall more favorable susceptibility profile; the highest resistance rates were observed for amoxicillin and potentiated sulfonamide, whereas all isolates were susceptible to ceftriaxone, colistin, and neomycin. The MDR rate in the Salmonella group was 20.0%, and neither extensively drug-resistant (XDR) nor pandrug-resistant (PDR) phenotypes were identified in either bacterial species.

Based on our results, antimicrobial resistance remains a relevant issue among clinical isolates from the Hungarian waterfowl sector. In the present sample, E. coli isolates showed a descriptively higher resistance burden than Salmonella isolates; however, none of the agent-specific between-species differences remained statistically significant after FDR correction. These findings support the need for targeted bacteriological and phenotypic susceptibility testing, as well as regular resistance monitoring, in the waterfowl sector.