Prevalence and Molecular Characteristics of Enterococci Isolated from Clinical Bovine Mastitis Cases in Ningxia

Jing Liu,1,* Zeyi Liang,1,* Maocao Zhongla,2 Hongsheng Wang,3 Xu Sun,4 Juanshan Zheng,1 Xuezhi Ding,1 Feng Yang1 1Key Laboratory of New Animal Drug Project of Gansu Province/Key Laboratory of Veterinary Pharmaceutics Discovery, Lanzhou Institute of Husbandry and Pharmaceutical Sciences of Chinese Academy of Agricultural Science, Lanzhou, People’s Republic of China; 2Gannan Animal Disease Prevention and Control Center, Hezuo, People’s Republic of China; 3Xiangyang Vocational and Technical College, Xiangyang, People’s Republic of China; 4College of Life Sciences and Engineering, Lanzhou University of Technology, Lanzhou, People’s Republic of China*These authors contributed equally to this workCorrespondence: Feng Yang; Xuezhi Ding, Lanzhou Institute of Husbandry and Pharmaceutical Sciences of Chinese Academy of Agricultural Science, No. 335 Jiangouyan, Qilihe District, Lanzhou, Gansu, 730050, People’s Republic of China, Tel +86-931-2115262, Fax +86-931-2114180, Email yangfeng@caas.cn; dingxuezhi@caas.cnPurpose: This study aimed to investigate the prevalence and genetic characterization of enterococcal isolates (Enterococcus faecalis, Enterococcus faecium and Enterococcus hirae) isolated from clinical bovine mastitis cases in Ningxia, China.Patients and Methods: The enterococci were identified by 16S rRNA amplification and sequencing. Antimicrobial resistance was determined by disc diffusion method. Virulence and antimicrobial resistance genes were detected by PCR assays.Results: Overall, 198 enterococcal isolates were identified from 2897 mastitis samples, including 137 (4.7%) E. faecalis, 50 (1.7%) E. faecium and 11 (0.4%) E. hirae. E. faecalis, E. faecium and E. hirae isolates showed high resistance to tetracycline (92.7%, 68.0%, 90.9%), followed by erythromycin (86.9%, 76.0%, 72.7%). The multidrug-resistant strains of E. faecalis and E. faecium were 29 (21.2%) and 13 (26.0%), respectively. The resistance of E. faecalis, E. faecium and E. hirae isolates to tetracycline is mainly attributed to the presence of tetL (alone or combined with tetM and/or tetK), the erythromycin resistance to ermB (alone or combined with ermC and/or ermA). Moreover, cpd (94.2%), gelE (77.4%), efaAfs (93.4%), and esp (79.6%) were the most common virulence genes in E. faecalis. In E. faecium, except for the gene efaAfs (82.0%), other virulence genes are rarely found. Only two strains of E. hirae carrying asa1 gene were detected.Conclusion: The results of this study can provide a reference for the prevention and treatment of bovine mastitis caused by enterococci.Keywords: bovine mastitis, enterococci, antimicrobial resistance, virulence