In vitro antimicrobial susceptibility of Mycoplasma hyorhinis field isolates collected from swine lung specimens in Korea

Mycoplasma hyorhinis is a very common inhabitant of the respiratory tract of pigs with or without pneumonia. Because there is no vaccine available to control M hyorhinis, chemotherapy is the most practical way to treat disease associated with M hyorhinis infection. Therefore, we tested the antimicrobial susceptibility of M hyorhinis isolates recovered from lung specimens of pigs using the liquid minimum inhibitory concentration (MIC) method in tests with 12 antimicrobial agents. The MIC50, MIC90, and range of MICs against 10 field isolates from Korea and the reference strain (ATCC 17981) were investigated. Mycoplasma hyorhinis field isolates were sensitive to lincomycin and tylosin but resistant to erythromycin, spectinomycin, and streptomycin. The MIC90s for lincomycin and tylosin were 0.5 µg per mL and 1.0 µg per mL, respectively. The MIC90s for amoxicillin, erythromycin, penicillin, spectinomycin, and streptomycin were ≥ 64 µg per mL. The MIC90s for gentamicin, kanamycin, and neomycin were 4.0 µg per mL, 8.0 µg per mL and 16 µg per mL, respectively. For oxytetracycline and tetracycline, the MIC50 was 4.0 µg per mL and the MIC90 was 16 µg per mL. These results provide practical information for treatment of M hyorhinis infection in pigs.