Aim: To determine the molecular epidemiology, genotypes and phenotypes of the major species of Streptococcus associated with bovine subclinical mastitis in Hainan, China.
Methods and results: In total, 150 subclinical mastitis milk samples were collected from two large dairy farms in Hainan. On the basis of biochemical tests and 16S rDNA sequencing, 39 samples were Streptococcus positive and the most frequently isolated species was Streptococcus uberis (n = 29, 74.4%). According to multilocus sequence typing (MLST), and assays of biofilm formation, antimicrobial susceptibility, resistance and virulence genes, the S. uberis isolates were clustered into nine new sequence types (STs; ST986-ST994) but were not merged into a clonal group (except for ST991 [CC143]). All isolates produced biofilm, but most weakly. The dominant virulence pattern was hasABC + sua + gapC + oppF + pauA + mtuA + cfu (27/29, 91.1%), based on the 11 virulence genes tested. The majority of isolates (88.46%) carried at least one resistance gene, and more than half (58.62%) were multidrug-resistant. The main resistance genes were linB (65.5%), ermB (37.9%) and tetS (34.5%), among the six antibiotic resistance genes and 11 antimicrobials tested.
Conclusion: Environmental S. uberis is important in bovine subclinical mastitis in Hainan.
Significance and impact of the study: Streptococcus uberis isolates in Hainan, China, show distinct MLST, virulence and antibiotic resistance characteristics.
Keywords: Streptococcus uberis; antimicrobial resistance; bovine subclinical mastitis; multilocus sequence typing; virulence.
© 2021 The Society for Applied Microbiology.