The Genetic Diversity Analysis Of Streptococcus Uberis Causing Bovine Mastitis In Sourthern Xinjiang

Streptococcus uberis is an environmental pathogen which can easily cause bovine subclinical mastitis. The infection caused by S. uberis is hard to cure after cows are breasted, and then results in significant economic losses. In this study, we detected a total of 259 milk samples, which were collected from 3 dairy farms in southern Xinjiang, using LMT(Lanzhou Mastitis Test). Then morphological and molecular methods were combined to isolate and identify S. uberis from subclinical mastitis cow milk samples. These tested strains were further analyzed using pulsed-field gel electrophoresis (PFGE) and multi- locus sequence typing (MLST) to reveal genetic diversity. The results showed that the amount of positive subclinical mastitis milk in tested 259 samples was 169, which occupied 65.3%, and 42 strains of Streptococci were isolated. With sequencing 16S rDNA gene, we found 28 isolates belonging to S. uberis, 9 isolates belonging to S. suis, 2 isolates belonging to S. lutetiensis, 1 isolate belonging to S. waiu and 2 isolates belonging to S. equinus. Analyzing 13 S. uberis strains from the 1st dairy farm by PFGE, we found that the DNA genomes of all strains could be digested fully with Apa I and Sma I respectively or together. Each electrophoresis profile ranged from 13 to 19 bands between the sizes of 15 kb-276 kb (Apa I, up to 14 bands; Sma I, up to 13 bands; Apa I and Sma I together, up to 19 bands). However, all strains showed the same PFGE type. Analyzing sequences of six candidate genes of 28 S. uberis strains, we found that each candidate gene had 3-5 different allele values. The results of MLST that S. uberis isolated from the 1st dairy farm had only unique sequence type ST158, S. uberis isolated from the 2nd dairy farm were divided into 5 sequence types: ST154(10%), ST155(50%), ST156(10%), ST157(20%) and ST159 (10%), and S. uberis isolated from the 3rd dairy farm had two different sequence types: ST22(80%) and ST153(20%). Consequently, the results revealed that strain genetic diversity emerged in S. uberis isolated from subclinical mastitis cows of southern Xinjiang.