Antimicrobial Susceptibility Profiles of Erysipelothrix rhusiopathiae and Riemerella anatipestifer Isolates from Clinical Cases of Waterfowl in Hungary Between 2022 and 2023.

Background:Riemerella anatipestifer and Erysipelothrix rhusiopathiae remain clinically significant pathogens in the waterfowl industry, causing substantial economic losses and posing potential zoonotic risks. Antimicrobial resistance (AMR) continues to spread in the poultry sector, making regular surveillance of bacterial isolates essential. Methods: In this study, eight R. anatipestifer and eighteen E. rhusiopathiae strains were isolated from clinical cases in Hungarian waterfowl between 2022 and 2023. Minimum inhibitory concentration (MIC) values were determined for antibiotics of veterinary and public health significance. Results: For R. anatipestifer, high resistance rates were observed for spectinomycin, lincomycin, and tiamulin, while beta-lactam antibiotics (amoxicillin, ceftriaxone, and imipenem) demonstrated strong efficacy. Among the E. rhusiopathiae isolates, resistance to amoxicillin (89%) and enrofloxacin (61%) was notable, whereas ceftriaxone and doxycycline exhibited moderate antibacterial effects. Conclusions: Our findings underscore the importance of targeted antimicrobial use in the waterfowl industry. Beta-lactam antibiotics remain effective, whereas rising resistance to fluoroquinolones and aminoglycosides raise serious concerns. Routine AMR surveillance and the adoption of alternative strategies are crucial for controlling infections and maintaining flock health.