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Mycoplasma hyorhinis is a common pathogen of swine causing mainly polyserositis and arthritis, but it has also been implicated as a cause of pneumonia. The economic losses due to M. hyorhinis infection could be reduced by antibiotic treatment. The aim of this study was to determine minimal inhibitory concentrations (MIC) of antibiotics potentially used to combat M. hyorhinis in swine production. Thirty-eight Hungarian M. hyorhinis strains isolated between 2014 and 2017 were examined by microbroth dilution tests for fifteen antimicrobial agents. Low MIC values of tetracyclines (MIC 50 0.078 μg/ml for doxycycline, ≤0.25 μg/ml for oxytetracycline) and pleuromutilins (MIC 50 0.156 μg/ml for tiamulin, ≤0.039 μg/ml for valnemulin) were detected against all strains. Fluoroquinolones (MIC 50 0.625 μg/ml), gentamicin (MIC 50 1 μg/ml) and florfenicol (MIC 50 2 μg/ml) inhibited the growth of Hungarian isolates at moderate MIC values. Most of the strains were inhibited by spectinomycin with low or moderate MIC values (MIC 50 4 μg/ml) except one strain (>64 μg/ml). Numerous isolates showed decreased susceptibility to macrolides and lincomycin (MIC 90 >64 for tylosin, tilmicosin, tulathromycin, gamithromycin, lincomycin, 8 μg/ml for tylvalosin). This study serves as evidence for the increasing resistance to macrolides and lincomycin in mycoplasmas, and also reports the occurrence of strains with extremely high MIC values to spectinomycin thus emphasizes the importance of the prudent use of antibiotics. Based on our results, tetracyclines and pleuromutilins are the most active compounds in vitro against the Hungarian M. hyorhinis strains., (Copyright © 2018 Elsevier B.V. All rights reserved.)

The molecular mechanisms of resistance to fluoroquinolones, tetracyclines, an aminocyclitol, macrolides, a lincosamide, a phenicol, and pleuromutilins were investigated in Mycoplasma bovis For the identification of mutations responsible for the high MICs of certain antibiotics, whole-genome sequencing of 35 M. bovis field isolates and 36 laboratory-derived antibiotic-resistant mutants was performed. In vitro resistant mutants were selected by serial passages of M. bovis in broth medium containing subinhibitory concentrations of the antibiotics. Mutations associated with high fluoroquinolones MICs were found at positions 244 to 260 and at positions 232 to 250 (according to Escherichia coli numbering) of the quinolone resistance-determining regions of the gyrA and parC genes, respectively. Alterations related to elevated tetracycline MICs were described at positions 962 to 967, 1058, 1195, 1196, and 1199 of genes encoding the 16S rRNA and forming the primary tetracycline binding site. Single transversion at position 1192 of the rrs1 gene resulted in a spectinomycin MIC of 256 μg/ml. Mutations responsible for high macrolide, lincomycin, florfenicol, and pleuromutilin antibiotic MICs were identified in genes encoding 23S rRNA. Understanding antibiotic resistance mechanisms is an important tool for future developments of genetic-based diagnostic assays for the rapid detection of resistant M. bovis strains., (Copyright © 2017 American Society for Microbiology.)