竹鼠源弗氏柠檬酸杆菌的分离鉴定及致病性分析

摘要

To identify the causative agent infecting the bamboo rats on a farm in the Guilin,a strain of bacterium was isolated from the liver of diseased bamboo rats.Its morphological characteristics and the results of 16S rRNA gene sequence analysis proved that the pathogenic bacteria was Citrobacter freundii.Phylogenetic analysis indicated that the isolate was closely related to C.freundii from a two-spotted spider mite,but it was an independent branch.In a pathogenic test,the isolate was pathogenic to adult mice,with a median lethal dose (LD50) of 2.8 × 108 CFU,and its LD50to 10-20 days old bamboo rats was 6.3 × 108 CFU.Results of antibiotic susceptibility testing demonstrated that the C.freundii was highly sensitive to ceftriaxone,gentamycin,amikacin,ofloxacin,levofloxacin,and was resistant to penicillin,cefazolin,florfenicol,lincomycin,deoxycycline.Histopathological observation showed that the bamboo rat's septum alveolus widened,accompanied by inflammatory cell infiltration,and angiectasis in liver and hyperemia.Outside the integument of spleen there were a large number of necrotic cells,and the swelling and granular degeneration of the renal tubular epithelial cells.These findings suggest that C.freundii is the pathogen of the dead bamboo rats in Guilin.The pathogenicity of the isolate to bamboo rats is strong.%为确定桂林某竹鼠养殖场患病竹鼠的病原,从发病竹鼠肝组织分离到一株细菌.根据形态学特征及16SrRNA基因序列分析,确定分离菌株为弗氏柠檬酸杆菌.进化分析显示,该菌与来自棉花红蜘蛛的弗氏柠檬酸杆菌遗传关系最近,但处于独立的分支上.毒力试验结果表明,该菌对成年小白鼠的LD5o为2.8×108 CFU,对10～20日龄的竹鼠LD50为6.3×108 CFU.药敏试验结果显示,分离菌株对头孢曲松、庆大霉素、阿米卡星、氧氟沙星、左氧氟沙星药物高度敏感,对青霉素、头孢唑啉、氟苯尼考、林可霉素、强力霉素等有耐药性.病理组织学观察显示,发病竹鼠肺泡间隔增宽伴随炎性细胞浸润;肝组织血管扩张、淤血;脾被膜外大量坏死细胞;肾组织肾小管上皮细胞肿胀、颗粒变性.综上研究结果表明,弗氏柠檬酸杆菌是引起桂林竹鼠发病和致死的病原菌,分离菌株对竹鼠有较强的致病性.