一株牛源约翰逊不动杆菌的分离鉴定

目的分离并鉴定1株致2018年7月四川省某肉牛场肉牛患呼吸道疾病并死亡的约翰逊不动杆菌。方法采集发病牛鼻腔拭子并从中分离得到一株优势菌株,对其进行形态学鉴定、生化鉴定、测定16s rRNA基因序列,用MEGA-X软件进行同源性分析、构建进化树,并进行药敏检测。结果分离菌为革兰染色阴性短杆菌,生化特性与约翰逊不动杆菌相符合,16S rRNA序列与GenBank中约翰逊不动杆菌株的同源性均达99%,因此将分离菌确定为约翰逊不动杆菌,并命名为ZZCNC-7B。8只SPF级昆明小鼠用1.4×10⁸ CFU/ml的ZZCNC-7B菌液腹腔注射(0.2 ml/只)后出现精神沉郁、腹式呼吸、眼部出现黏性分泌物、眼睑粘连、畏寒抱团等症状,有6只小鼠在16~36 h内死亡,另2只小鼠出现相同的症状但仍存活。剖检死亡小鼠,大体观察肺、肾充血肿大;肝、脾淤血肿大,肠道积气积液;组织学观察肺充血、出血,肝淤血,脾淤血、出血,肾小管坏死等病变。药敏试验显示,分离菌对四环素类药物四环素和磺胺类药物磺胺异恶唑耐药,对氨苄西林、亚胺培南、左氧氟沙星以及庆大霉素等药物均敏感。结论病牛分离菌为约翰逊不动杆菌,对小鼠具有较强的致病性和致死性,可引起肉牛呼吸道感染,甚至导致肉牛死亡,应引起高度重视。

Isolation and identification of a bovine Acinetobacter johnsonii strain

Objectives To isolate and identify a strain of Acinetobacter johnsonii causing respiratory disease and death of beef cattle in a cattle farm in Sichuan Province in July 2018.Methods A dominant strain was isolated from nasal swabs from diseased cattle,and its morphological and biochemical characteristics and 16 S rRNA gene sequence were determined.A homology analysis was performed using the software MEGA-X,an evolutionary tree was constructed,and drug susceptibility was determined.Results The isolates were a Gram-negative brevibacterium with biochemical characteristics consistent with A.johnsonii.The 16 S rRNA sequence had 99%similarity to the A.johnsonii strain in GenBank.Therefore,the isolates were identified as A.johnsonii and designated ZZCNC-7 B.Eight SPF Kunming mice were intraperitoneally injected with 1.4×10⁸ CFU/mL of a ZZCNC-7 B bacterial solution(0.2 mL/mouse).Mice developed depression,abdominal breathing,viscous secretions in the eyes,eyelid adhesions,an aversion to cold,they huddled together,and other symptoms.Six mice died within 16-36 h of infection,while the other two mice exhibited the same symptoms but survived.The dead mice were dissected,with hyperemia and swelling of the lungs and kidneys,congestion and swelling of the liver and spleen,and pneumatosis and fluid accumulation in the gastrointestinal tract.Histological observations revealed lung hyperemia and hemorrhage,liver congestion,spleen congestion and hemorrhage,and renal tubule necrosis.Drug sensitivity tests indicated that the isolates were resistant to tetracyclines and sulfisoxazole,and sensitive to ampicillin,imipenem,levofloxacin,and gentamicin.Conclusion The isolates from diseased cattle are A.johnsonii,they are highly pathogenic and lethal to mice,and they can cause a respiratory tract infection or even death in beef cattle,so considerable attention should be paid to this pathogen.