Mycoplasma synoviae infection causes infectious synovitis and respiratory disease in broilers and a reduction in egg production and eggshell apex abnormalities (EAA) in layers, with widespread prevalence in the Chinese mainland since 2010. However, data on this pathogen in Chongqing remain scarce. The present study aimed to investigate the prevalence, sequence types (STs), hemagglutination activity, pathogenicity, and susceptibility to antimicrobials and Chinese herbal monomers of M. synoviae isolates from broilers and layers mainly in Chongqing. Additionally, we analyzed the genotype–phenotype correlations underlying the resistance of these isolates to fluoroquinolones and macrolides. A total of 23 M. synoviae isolates were recovered from 148 Chinese indigenous broilers, and 22 isolates were obtained from 210 eggs with EAA, yielding 45 isolates totally. These isolates were classified into five novel STs, namely ST196, ST258, ST261, ST264, and ST265. Phylogenetic analysis indicated that isolates belonging to the same ST formed distinct monophyletic clusters, and all isolates shared the closest genetic affinity with strains previously isolated in China. Of the 45 isolates, 42.2% were able to agglutinate chicken erythrocytes. All isolates were susceptible to doxycycline, tylvalosin, tilmicosin, lincomycin, and tiamulin but uniformly resistant to enrofloxacin. The majority of isolates displayed minimum inhibitory concentration (MIC) values >4 μg/mL for amikacin (97.8%), apramycin (93.3%), and erythromycin (91.1%). Notably, the Chinese herbal monomer berberine hydrochloride exhibited potent anti‐ M. synoviae activity, with an MIC range of 2–32 μg/mL. Genotypic analysis identified mutations in the parC gene (A56T, T85I, N89D) and ribosomal protein L4 (I174V, N215S), which were associated with the resistance of isolates to enrofloxacin and erythromycin, respectively. Both joint‐ and egg‐derived isolates induced infectious synovitis and caseous exudates in specific pathogen‐free (SPF) chickens. These findings highlight M. synoviae genetic/phenotypic diversity in Chongqing, emphasizing the need for rational antimicrobial stewardship to curb drug‐resistant M. synoviae isolates.
Wang et al. (2026) studied this question.