Genetic diversity of Streptococcus uberis isolates from dairy cows with subclinical mastitis in Southern Xinjiang Province, China

Abstract

Streptococcus uberis is a common cause of dairy cow mastitis throughout the world. The failure to control bovine mastitis caused by S. uberis is largely attributed to the little known about the epidemiology of this bacteria, especially strain differences in the same area. To define the local epidemiology of S. uberis in the south of Xinjiang, China, we explored the genetic diversity of 28 bovine subclinical mastitis field isolates of S. uberis, collected from 3 Chinese farms during 2009 and 2010, which was examined by using pulsed-field gel electrophoresis (PFGE) for clustering of the isolates and multilocus sequence typing (MLST) to assess the relationship between PFGE patterns and to identify genetic lineages. The 28 isolates were grouped into 13 pulsotypes (U1 to U13), and 1 PFGE type (U1) accounted for almost half of the isolates (13/28, 46.4%). This major type was herd specific, indicating either cow-to-cow transmission or infection with isolates from the same environmental reservoirs. The remaining 12 PFGE types of isolates were from different herds, strongly suggesting environmental sources of S. uberis infection. All 28 isolates were analyzed by MLST and clustered into 8 sequence types (STs), of which 7 STs were found to be novel, either with 5 new alleles of 6 housekeeping and virulence genes (ST158, ST159) or with different combinations of previously assigned alleles (ST153, ST154, ST155, ST156, ST157). To our knowledge, this is the first report that documents molecular typing studies of bovine isolates of S. uberis from southern Xinjiang Province, China, which were shown to represent novel genomic backgrounds of this pathogen.