Identification of Shigella boydii in Yak and Its Pathogenicity to BALB/c Mice

The aim of this study is to identify Shigella isolated from healthy slaughter yak,and to determine its pathogenicity to mice.The isolate was identified and eventually characterized by using several methods,including morphology observation,culture characteristics,biochemical tests,serotyping,16S rRNA sequencing,electron microscopy and evaluation of pathogenicity to BALB/c mice.The results showed that morphological,culture and biochemical characteristics of the isolate is consistent with that of Shigella.The isolate was serotyped as Shigella boydii type 6.Phylogeny analysis based on 16S rRNA indicated that the isolate has close relationship with Shigella boydii and Shigella sonnei in human,and has further relationship with the Shigella from other animals.The isolate is pathogenic to BALB/c mice,and the LD50 is 2.5×107.5CFU.The bacterium is not resistant to antibiotics commonly used.We isolated Shigella boydii type 6 from yak for the first time.The isolate is highly pathogenic and phylogentically related to human Shigella,indicating important significance of yak Shigella in public health.