Infection status of Mycoplasma gallisepticum and Mycoplasma synoviae and antimicrobial susceptibility of Mycoplasma isolates from a large-scale chicken farm in Guangdong Province

Mycoplasma gallisepticum (MG) and Mycoplasma synoviae (MS) are two major mycoplasma diseases that cause illness in chickens in the poultry industry. In addition, there are some mycoplasma species with lower pathogenicity such as Mycoplasma gallinarum (MGn) and Mycoplasma gallinaceum (MGC). MG and MS lead to respiratory diseases, synovitis, and airsacculitis, causing significant economic losses. However, data on the prevalence and antimicrobial susceptibility of the isolated Mycoplasma strains in large-scale farms in South China are limited. This study investigated the infection rates of MG and MS in a large-scale chicken farm in Guangdong Province using PCR targeting the 16 S rDNA gene on 2,040 oropharyngeal swab samples. Subsequently, mycoplasma isolation and culture, antimicrobial susceptibility testing (MIC), embryo pathogenicity assay, and molecular typing of MS isolates based on the vlhA gene were performed. The results showed that the positive rates of MG in breeder chickens and commercial chickens were 5.5% and 31.5%, respectively, and those of MS were 14.8% and 46.2%, respectively. A total of 5 MS strains, 4 MGn strains, and 4 MGC strains were isolated. In a preliminary experiment with a limited sample size ( n = 3 per group), no embryo mortality was observed in the MGC and MGn groups, but claw curling was noted. The isolated MS strains were all of the L type, and MIC results indicated that the clinical strains showed reduced susceptibility to enrofloxacin, doxycycline, tylosin, and tilmicosin compared with the reference strain WVU1853. These findings indicate that MG and MS infections are prevalent on this farm, and the isolated MS, MGC, and MGn strains showed reduced susceptibility to several antibiotics compared with the reference strain WVU1853.