Antimicrobial susceptibility profiles of Mycoplasma hyosynoviae strains isolated from five European countries between 2018 and 2023.

Mycoplasma (M.) hyosynoviae is a facultative pathogen, causing arthritis in finisher pigs world-wide. In the absence of a commercial vaccine improvement of housing conditions and antibiotic therapy are the only options to alleviate the clinical signs. This study aimed to determine antibiotic susceptibility profiles of 106 M. hyosynoviae isolates against ten antibiotics licensed for veterinary use in cases of arthritis. The isolates were collected between 2018 and 2023 from five European countries: Austria (n = 20), Belgium (n = 20), Germany (n = 25), Hungary (n = 21) and Italy (n = 20). The minimal inhibitory concentrations (MIC) were determined by broth micro-dilution assay. The tested isolates were highly susceptible to tiamulin (MIC90 ≤ 0.039 µg/ml), tylvalosin (MIC90 ≤ 0.039 µg/ml) and lincomycin (MIC90 ≤ 0.25 µg/ml). Low concentrations of tylosin (MIC90 0.5 µg/ml) and tilmicosin (MIC90 1 µg/ml) inhibited the growth of the isolates. While moderate minimal inhibitory concentrations were detected for doxycycline (MIC90 0.312 µg/ml), oxytetracycline (MIC90 2 µg/ml), enrofloxacin (MIC90 0.625 µg/ml) and florfenicol (MIC90 2 µg/ml), only high concentrations of tulathromycin (MIC90 64 µg/ml) inhibited the growth of the isolates. Statistical analysis revealed significant differences between countries in case of enrofloxacin, where the Hungarian isolates showed the lowest MIC values, and the German isolates the highest MIC values among the tested countries. Our results show that European M. hyosynoviae isolates are generally susceptible to the tested antibiotics with the exception of tulathromycin. The country specific differences indicate the importance of regular susceptibility testing of isolates on a Pan-European level.