Abstract: To investigate the cause of the disease and death of Simmental beef cattle from a large-scale farm in Malong County，Yunnan Province，PCR tests were carried out on some bovine virus diseases（BVDV、BCV、BAdV-7、 BAdV-3、BRSV and BEFV）and bacterial pathogens（MB and Pasteurella pultocida）in the lung tissues of the sick and dead cattle sent for testing，followed by bacteria isolation，purification，Gram stained，biochemical identification and antimicrobial susceptibility testing. The results showed that the nucleic acid and bacterial PCR test results of the tested bovine virus were negative. The isolated and purified bacteria were Gram - negative short rods，biochemically characterized as Mannheimella hemolytica. Antimicrobial susceptibility testing revealed sensitivity to polymyxin B and resistant to spectinomycin，chloramphenicol，cefoperazone，cefotaxime，minocycline，ceftriaxone，ceftazidime and cefuroxime. These findings provide theoretical reference for the effective diagnosis and treatment of“ shipping fever” （bovine Mannheimella hemolytica infection，either single or mixed）

Key words: Cattle, Mannheimella hemolytica, Separation and identification, Antimicrobial resistance

摘要： 为查明导致云南省马龙县某规模化肉牛场饲养西门塔尔肉牛发病死亡的病因，对送检病死牛肺脏组织进行部分牛病毒病（病毒性腹泻病毒、冠状病毒、腺病毒3型、腺病毒7型、呼吸道合胞体病毒和流行热病毒）和细菌病（牛支原体和多杀巴氏杆菌）PCR检测，并进行细菌分离纯化、革兰氏染色、生化鉴定及药敏试验。结果显示，被检牛病毒核酸和细菌PCR检测结果均为阴性；分离纯化得到的细菌为革兰氏阴性短杆菌，经生化鉴定为溶血性曼海姆菌，该细菌对多粘菌素B敏感，对大观霉素、氯霉素、头孢哌酮、头孢噻肟、米诺环素、头孢曲松、头孢他啶和头孢呋辛耐药。该试验研究结果可为动物“运输热”（牛溶血性曼海姆菌单纯或混合感染）的有效诊疗及防治提供理论参考。

关键词: 牛, 溶血性曼海姆菌, 分离鉴定, 耐药性