Abstract: To explore the pathogenic mechanism and drug resistance characteristics of Shigella flexneri in duck hosts，one suspected pathogenic bacterium strain was isolated from the intestinal tissues of dead ducks submitted for inspection from a duck farm in Henan Province. The typical single colony was selected after inoculation with LB agar plate medium. Gram staining microscopy，16S rRNA gene sequence amplification and sequencing analysis were used to identify the strain.Subsequently，the pathogenicity test was carried out by using the mouse model of intragastric infection，and the intestinal tissue was observed by hematoxylin‑eosin staining.At the same time，the drug sensitivity analysis was carried out by agar diffusion method and microdilution method. The results showed that the strain was gram‑negative short bacilli in morphology，and its 16S rRNA gene sequence was located in the same evolutionary branch as Shigella flexneri with GenBank accession number NR026331.1.The strain was identified as Shigella flexneri and named B25.Moreover，infection with the B25 strain could cause severe lesions in the intestinal tract of mice，which were manifested as complete shedding of intestinal epithelial cells，atrophy and fracture of villus structure，infiltration of inflammatory cells（such as lymphocytes and neutrophils）in mucosal layer and local hemorrhage and necrosis. The median lethal dose was 7.7×10⁵ cfu/mL. Drug sensitivity tests indicated that the bacterium was resistant to amoxicillin［minimum inhibitory concentration（MIC）>2 048 μg/mL］，doxycycline（MIC>64 μg/mL），cefoxitin（MIC>80 μg/mL），ceftazidime（MIC>160 μg/mL） and gentamicin（MIC>20 μg/mL），sensitive tomeropenem（MIC<0.04 μg/mL）and fosfomycin（MIC<40 μg/mL），and moderately sensitive to polymyxin（MIC=0.1 μg/mL）.In summary，this study reveals that the duck‑derived Shigella flexneri B25 has multiple drug resistance and strong pathogenicity，which can provide a scientific basis for the diagnosis and the prevention and control strategy formulation of bacterial dysentery in duck farms.

Key words: Duck, Shigella flexneri, Isolation and identification, Pathogenicity, Drug sensitive test, 16S rRNA

摘要： 为探究福氏志贺菌在鸭源宿主中的致病机制和耐药特征，从河南省某鸭场送检的病死鸭肠道组织中分离得到一株疑似致病菌，采用LB琼脂平板培养基接种，革兰氏染色镜检、16S rRNA基因序列扩增与测序分析等方法对其进行鉴定；随后进一步采用小鼠灌胃感染致病菌模型开展致病性试验、对肠组织进行苏木精-伊红染色病理观察，同时通过琼脂扩散法和微量稀释法进行药物敏感性分析。结果表明，该菌株形态为革兰阴性短杆菌，其16S rRNA基因序列与GenBank登录号NR026331.1的福氏志贺菌位于同一进化分支，确定该菌株为福氏志贺菌并命名为B25。B25菌株感染后可导致小鼠肠道出现严重病变，具体表现为肠上皮细胞完全脱落、绒毛结构萎缩断裂、黏膜层炎症细胞（如淋巴细胞和中性粒细胞）浸润及局部出血坏死，其半数致死量（LD₅₀）为7.7×10^⁵ cfu/mL。药物敏感性测试表明，该菌对阿莫西林［最小抑菌浓度（MIC）>2 048 μg/mL］、多西环素（MIC>64 μg/mL）、头孢西丁（MIC>80 μg/mL）、头孢他啶（MIC>160 μg/mL）、庆大霉素（MIC>20 μg/mL）表现为耐药，对美罗培南（MIC<0.04 μg/mL）和磷霉素（MIC<40 μg/mL）敏感，对多黏菌素（MIC=0.1 μg/mL）呈中度敏感。综上，揭示了鸭源福氏志贺菌B25具备多重耐药性和较强致病性，可为鸭场细菌性痢疾的诊断、防控策略制定提供科学依据。

关键词: 鸭, 福氏志贺菌, 分离鉴定, 致病性, 药敏试验, 16S rRNA