Abstract: Molecular identification and drug susceptibility of a strain pathogenic bacteria isolated from a yak suffered from bleeding from a farm of Naqu city,Tibet,were analyzed,in order to provide treatment bases for hemorrhagic disease of yaks in Tibet.The suspected strains were obtained by bacterial isolation and purification from lungs and livers of dead yaks,then the suspected strains were screened out by morphological observation and Columbia blood plate test,and then physiological and biochemical tests were done,16S rDNA sequencing and homology comparison test on the obtained suspected strains,and then obtained sensitive drugs of the suspected pathogenic strains by drug sensitivity tests,finally verified treatment effect of the sensitive drugs by animal regression test.The results showed that 6 suspected strains were obtained by separation and purification of the lungs and livers of dead yaks,and a strain of hemolytic Gram-positive cocci S-4 was screened out by morphological observation test and Columbia blood plate test,and the S-4 strain was identified as Staphylococcus epidermidis by the physiological and biochemical identification test,16S rDNA sequencing,homology comparison test.The drug sensitivity test showed that the S-4 strain was sensitive to enrofloxacin,neomycin,polymyxin B,kanamycin,and ciprofloxacin.And it was medium sensitive to florfenicol and doxycycline.And it was tolerant to streptomycin,erythromycin,tetracycline,penicillin and cephalexin.The animal regression tests showed that the strain was pathogenic and enrofloxacin,neomycin,and kanamycin,the 3 drugs had good treatment effects,while polymyxin B and ciprofloxacin had poor treatment effects.The results showed that this experiment obtained a pathogenic Staphylococcus epidermidis from yaks,the pathogenic bacteria could be treated with enrofloxacin,neomycin,and kanamycin during the breeding.

Key words: yak source; isolation and identification; Staphylococcus epidermidis; drug sensitivity test