Avian pathogenic Escherichia coli (APEC) is an important pathogen that causes avian colibacillosis in poultry. APEC infection can lead to pathological changes in chicken trachea. The type VI secretion system (T6SS) of APEC contribute to the pathogenicity of APEC. However, whether T6SS plays a role in infection of the trachea remains unclear. We constructed mutant strain Δhcp2a by the Red recombination method system. The role of hcp2a (the structural secretion components and secretory protein of the T6SS) in the infection of trachea was investigated. The mutation strain displayed a significant increase in biofilm formation and a decrease in resistance to chicken serum. Moreover, RNA sequencing analyses showed that infection of chicken tracheal epithelium by the mutant strain Δhcp2a induced differential expression of genes. The result also showed that 14 genes (13 genes were downregulated) were enriched in cytokine-cytokine receptor interaction signalling pathway at 12 and 24 h post infection. The mutation Δhcp2a resulted in significant decreases in the bacterial loads in trachea at 6 and 12 h post infection. Real-time PCR analyses showed that the hcp2a mutation downregulated the expression of IL8 and IL1β at mRNA level in chicken tracheal epithelium. Our results indicate that mutation of hcp2a influenced genes expression of the cytokine-cytokine receptor interaction pathway by decreasing APEC colonization in the trachea.

禽致病性大肠杆菌（APEC）是导致禽大肠杆菌病家禽的重要病原菌。APEC感染可导致鸡气管发生病理变化。APEC的VI型分泌系统（T6SS）有助于APEC的致病性。然而，尚不清楚T6SS是否在气管感染中起作用。我们通过Red重组方法系统构建了突变株Δhcp2a。hcp2a的作用研究了气管感染中T6SS的结构分泌成分和分泌蛋白。突变菌株显示出生物膜形成的显着增加和对鸡血清的抗性降低。此外，RNA测序分析表明突变株Δhcp2a感染鸡气管上皮会诱导基因差异表达。结果还表明，在感染后12和24 h，细胞因子-细胞因子受体相互作用信号通路中富集了14个基因（13个基因被下调）。突变Δhcp2a导致感染后6和12 h气管中的细菌负荷显着降低。实时PCR分析显示hcp2a突变在鸡气管上皮中下调mRNA水平上IL8和IL1β的表达。我们的结果表明，hcp2a的突变通过减少气管中的APEC定植影响了细胞因子-细胞因子受体相互作用途径的基因表达。