TDK conference 2025

Streptococcus suis is a globally significant swine pathogen that can also be transmitted to humans as a zoonosis. Antibiotics play a crucial role in therapy, however, due to the increasing prevalence of resistance, regular susceptibility testing is essential. The aim of our study was to map the antimicrobial resistance status of S. suis isolates originating from Hungarian pig herds.

A total of 44 S. suis strains isolated from nasal swabs of clinically healthy swine were examined. Phenotypic antimicrobial susceptibility testing was performed using broth microdilution against 14 different agents, following the EUCAST and the CLSI guidelines. Minimum inhibitory concentrations (MIC) were determinded and MIC50 and MIC90 values were also calculated.

Our results showed that most β-lactam antibiotics (penicillin, amoxicillin, amoxicillin-clavulanate, ceftiofur, cefquinome) proves effective, altough 20,4% resistance was observed to penicillin. High susceptibility rates (>90%) were also detected for enrofloxacin and florfenicol. In contrast, tetracyclines (oxytetracycline, doxycycline) and the potentiated sulfonamide trimethoprim-sulfamethoxazole showed high resistance levels (54,5-59,1%). Macrolides (tilmicosin, tulathromycin), lincomycin and tiamulin also showed unfavorable MIC values, indicating limited effectiveness.

Overall, ceftiofur proved to be the most effective option in the therapy of S. suis. Tetracyclines and potentiated sulfonamides should be avoided due to the high resistance rates. Our research can contribute to more responsible antibiotic choices and the fight against antimicrobial resistance.