中文摘要：

目的构建鸡致病性大肠杆菌qseC基因缺失突变株和鸡致病性大肠杆菌qseC基因缺失互补株，并探讨qseC基因缺失对鸡致病性大肠杆菌生物学特性的影响。方法构建qseC基因缺失突变株和qseC基因缺失互补株并验证；绘制鸡致病性大肠杆菌野生株、qseC基因缺失突变株和qseC基因缺失互补株的生长曲线，并进行体外竞争试验、血凝试验和荧光定量PCR分析。结果qseC基因缺失突变株和qseC基因缺失互补株构建正确。生长曲线显示，qseC基因缺失突变株相对于野生株的生长速度降低，qseC基因缺失互补株的生长速度显著提高，但并没有完全达到野生株的水平。野生株和qseC基因缺失突变株体外竞争试验竞争参数值为0．67，野生株和qseC基因缺失互补株体外竞争试验竞争参数为1．14。相对于野生株，qseC基因缺失突变株的血凝滴度下降50％，I型菌毛相关基因表达下调；qseC基因缺失互补株的血凝滴度达到野生株水平，且部分I型菌毛相关基因表达上升。结论鸡致病性大肠杆菌qseC基因缺失降低了鸡致病性大肠杆菌的生长速度、生长能力以及对豚鼠红细胞的粘附能力。

英文摘要：

The influence of the qseC gene on the biological characteristics of avian pathogenic Escherichia coli （APEC） was investigated in our study. The qseC gene mutant （WT△qseC） and its complement strain （WT△qseC： pBADqseC） were con- structed. Then, the growth curves for WT, WT△qseC and WT△qseC： pBADqseC were depicted, and the in vitro competition assay, hemagglutination assay and fluorescent quantitative PCR were performed. The results indicated that WT△qseC and WT△qseC： pBADqseC were successfully constructed. The growth curves revealed that WT△qseC grew slowly compared to that of WT. The WT△qseC： pBADqseC restored its growth ability, but not to a perfectly normal level. The competition index value of WT and WT△qseC in vitro competition assay was 0.67, while that of WT△qseC and WT△qseC： pBADqseC was 1.14. Com- pared to WT, the average titer of WT△qseC decreased 50%, and the type I pill-related genes of WT△qseC were down regula- ted. The average titer of WT△qseC： pBADqseC restored to the level of WT, and the type I pill-related genes were upregulated in WT△qseC： pBADqseC, compared with WT△qseC. In conclusion, the growth rates, ability and the adherences to the normal guinea pig erythrocytes of APEC decreased in the absence of qseC gene.