The role of the wzy gene in lipopolysaccharide biosynthesis and pathogenesis of avian pathogenic Escherichia coli

Avian pathogenic Escherichia coli (APEC) causes severe respiratory and systemic diseases in poultry. The wzy gene encodes the O-antigen polymerase (Wzy), which plays an important role in the synthesis of the lipopoly-saccharide (LPS) of bacteria. However, the function of the wzy gene in APEC remains unclear. Hence, in this study, a strain harboring a wzy gene mutant (DE17 Delta wzy) was constructed and the characteristics of this strain were analyzed. The results showed that mutant of wzy changed the phenotype of the LPS and affected serum agglutination of the O-antigen. Decreased motility and biofilm formation was also observed, but the endotoxin titer of the LPS in APEC was not affected. In addition, the wzy mutation significantly decreased the adherence and invasion to DF-1 cells, especially the survival abilities in duck serum and complement. Furthermore, an LD50 assay revealed that the virulence of mutant strain DE17 Delta wzy was attenuated 132-fold compared with wild-type strain DE17. Moreover, the bacterial load in the blood, liver, spleen, and kidneys of ducks infected with DE17 Delta wzy was decreased significantly compared with wild-type strain DE17 (p < 0.0001). These results confirmed that the wzy gene is associated with LPS biosynthesis and bacterial pathogenicity in APEC.