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

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