Antibiotic resistance of Mycoplasma Synoviae strains isolated in China from 2016 to 2019

BACKGROUND: In the past decade, Mycoplasma synoviae (M. synoviae) infection has become widely prevalent in China, has caused serious economic losses and has become one of the most important diseases in the chicken industry. Medication is a general approach for the control of M. synoviae infection, but antibiotics are sometimes ineffective in clinical practice. To investigate the sensitivity of M. synoviae to antimicrobials commonly used in the treatment of M. synoviae infection, the antibiotic susceptibility of 32 M. synoviae strains isolated from China from 2016 to 2019 were determined using the minimum inhibitory concentration (MIC) method. RESULTS: All isolates had low MIC values for the combination of lincomycin and spectinomycin, pleuromutilin, and macrolides. However, the M. synoviae isolates displayed variance in MICs for doxycycline hydrochloride with a range of 0.25 to 8 μg/mL, and oxytetracycline hydrochloride with a range of 0.5 to 8 μg/mL. Three and one M. synoviae isolates showed intermediate MIC values to doxycycline hydrochloride and oxytetracycline hydrochloride, respectively. High MIC values for enrofloxacin were detected in all isolates with MICs ranging from 4 to 32 μg/mL. Furthermore, comparison of the parC QRDR identified a mutation at nucleotide position 254 (C254T) resulting in a Thr 85 Ile amino acid change in all M. synoviae isolates and the reference strain ATCC 25204 being resistant to enrofloxacin. Moreover, mutations at Glu 804 Gly and Thr 686 Ala of gyrA QRDR were identified in all M. synoviae isolates and ATCC 25204. The mutation in the QRDR of the parE gene resulted in amino acid changes at positions 197 (Pro to Ser) in 27/32 M. synoviae isolates. CONCLUSION: Three nonsynonymous mutations in gyrA and parE were first identified to be related to enrofloxacin resistance. Our results showed that M. synoviae resistance to enrofloxacin is widespread.